Merge pull request #32403 from obsidiansystems/gcc-modernize-builder

gcc: Modernize builder

8 files changed, 374 insertions, 400 deletions

diff --git a/pkgs/development/compilers/gcc/4.5/default.nix b/pkgs/development/compilers/gcc/4.5/default.nix
index 12739682292ba..b41d22f4f5398 100644
--- a/pkgs/development/compilers/gcc/4.5/default.nix
+++ b/pkgs/development/compilers/gcc/4.5/default.nix
@@ -25,6 +25,7 @@
 , libpthread ? null, libpthreadCross ? null  # required for GNU/Hurd
 , stripped ? true
 , buildPlatform, hostPlatform, targetPlatform
+, buildPackages
 }:
 
 assert langJava     -> zip != null && unzip != null
@@ -258,6 +259,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++
 
     # Basic configuration
     [
@@ -349,29 +352,32 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, cross != null
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
   LD = "ld";
   CC = "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -382,39 +388,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${libcCross.dev}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${libcCross.dev}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru = { inherit langC langCC langAda langFortran langVhdl
       enableMultilib version; isGNU = true; };
diff --git a/pkgs/development/compilers/gcc/4.8/default.nix b/pkgs/development/compilers/gcc/4.8/default.nix
index 51fb1a1c9a1e5..8713c174d5a6a 100644
--- a/pkgs/development/compilers/gcc/4.8/default.nix
+++ b/pkgs/development/compilers/gcc/4.8/default.nix
@@ -33,6 +33,7 @@
 , gnused ? null
 , darwin ? null
 , buildPlatform, hostPlatform, targetPlatform
+, buildPackages
 }:
 
 assert langJava     -> zip != null && unzip != null
@@ -316,6 +317,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++
 
     # Basic configuration
     [
@@ -372,14 +375,6 @@ stdenv.mkDerivation ({
     # Ada
     optional langAda "--enable-libada" ++
 
-    # Cross-compilation
-    optional (targetPlatform == hostPlatform) (
-      let incDir = if hostPlatform.isDarwin
-                     then "${darwin.usr-include}"
-                     else "${getDev stdenv.cc.libc}/include";
-      in "--with-native-system-header-dir=${incDir}"
-    ) ++
-
     platformFlags ++
     optional (targetPlatform != hostPlatform) crossConfigureFlags ++
     optional (!bootstrap) "--disable-bootstrap" ++
@@ -444,12 +439,12 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, targetPlatform != hostPlatform
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
     buildFlags = "";
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
@@ -457,18 +452,21 @@ stdenv.mkDerivation ({
   # http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210
   CC = if stdenv.system == "x86_64-solaris" then "gcc -m64" else "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -479,39 +477,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${getDev libcCross}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${libcCross.dev}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru =
     { inherit langC langCC langObjC langObjCpp langAda langFortran langVhdl langGo version; isGNU = true; };
diff --git a/pkgs/development/compilers/gcc/4.9/default.nix b/pkgs/development/compilers/gcc/4.9/default.nix
index 57d173c3a1444..c338f9c641ee6 100644
--- a/pkgs/development/compilers/gcc/4.9/default.nix
+++ b/pkgs/development/compilers/gcc/4.9/default.nix
@@ -33,6 +33,7 @@
 , gnused ? null
 , darwin ? null
 , buildPlatform, hostPlatform, targetPlatform
+, buildPackages
 }:
 
 assert langJava     -> zip != null && unzip != null
@@ -314,6 +315,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++
 
     # Basic configuration
     [
@@ -370,14 +373,6 @@ stdenv.mkDerivation ({
     # Ada
     optional langAda "--enable-libada" ++
 
-    # Cross-compilation
-    optional (targetPlatform == hostPlatform) (
-      let incDir = if hostPlatform.isDarwin
-                     then "${darwin.usr-include}"
-                     else "${getDev stdenv.cc.libc}/include";
-      in "--with-native-system-header-dir=${incDir}"
-    ) ++
-
     platformFlags ++
     optional (targetPlatform != hostPlatform) crossConfigureFlags ++
     optional (!bootstrap) "--disable-bootstrap" ++
@@ -442,12 +437,12 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, targetPlatform != hostPlatform
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
     buildFlags = "";
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
@@ -455,18 +450,21 @@ stdenv.mkDerivation ({
   # http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210
   CC = if stdenv.system == "x86_64-solaris" then "gcc -m64" else "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -477,39 +475,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${getDev libcCross}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${getDev libcCross}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru =
     { inherit langC langCC langObjC langObjCpp langAda langFortran langVhdl langGo version; isGNU = true; };
diff --git a/pkgs/development/compilers/gcc/5/default.nix b/pkgs/development/compilers/gcc/5/default.nix
index a34d14e880213..552e827ec366b 100644
--- a/pkgs/development/compilers/gcc/5/default.nix
+++ b/pkgs/development/compilers/gcc/5/default.nix
@@ -329,6 +329,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++ 
 
     # Basic configuration
     [
@@ -380,14 +382,6 @@ stdenv.mkDerivation ({
     # Ada
     optional langAda "--enable-libada" ++
 
-    # Cross-compilation
-    optional (targetPlatform == hostPlatform) (
-      let incDir = if hostPlatform.isDarwin
-                     then "${darwin.usr-include}"
-                     else "${getDev stdenv.cc.libc}/include";
-      in "--with-native-system-header-dir=${incDir}"
-    ) ++
-
     platformFlags ++
     optional (targetPlatform != hostPlatform) crossConfigureFlags ++
     optional (!bootstrap) "--disable-bootstrap" ++
@@ -452,12 +446,12 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, targetPlatform != hostPlatform
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
     buildFlags = "";
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
@@ -465,18 +459,21 @@ stdenv.mkDerivation ({
   # http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210
   CC = if stdenv.system == "x86_64-solaris" then "gcc -m64" else "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -487,39 +484,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${getDev libcCross}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${getDev libcCross}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru =
     { inherit langC langCC langObjC langObjCpp langAda langFortran langVhdl langGo version; isGNU = true; };
diff --git a/pkgs/development/compilers/gcc/6/default.nix b/pkgs/development/compilers/gcc/6/default.nix
index 61e7647f968f4..fbc4900260675 100644
--- a/pkgs/development/compilers/gcc/6/default.nix
+++ b/pkgs/development/compilers/gcc/6/default.nix
@@ -34,6 +34,7 @@
 , cloog # unused; just for compat with gcc4, as we override the parameter on some places
 , darwin ? null
 , buildPlatform, hostPlatform, targetPlatform
+, buildPackages
 }:
 
 assert langJava     -> zip != null && unzip != null
@@ -330,6 +331,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++
 
     # Basic configuration
     [
@@ -381,14 +384,6 @@ stdenv.mkDerivation ({
     # Ada
     optional langAda "--enable-libada" ++
 
-    # Cross-compilation
-    optional (targetPlatform == hostPlatform) (
-      let incDir = if hostPlatform.isDarwin
-                     then "${darwin.usr-include}"
-                     else "${getDev stdenv.cc.libc}/include";
-      in "--with-native-system-header-dir=${incDir}"
-    ) ++
-
     platformFlags ++
     optional (targetPlatform != hostPlatform) crossConfigureFlags ++
     optional (!bootstrap) "--disable-bootstrap" ++
@@ -452,12 +447,12 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, targetPlatform != hostPlatform
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
     buildFlags = "";
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
@@ -465,18 +460,21 @@ stdenv.mkDerivation ({
   # http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210
   CC = if stdenv.system == "x86_64-solaris" then "gcc -m64" else "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -487,39 +485,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${getDev libcCross}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${getDev libcCross}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru =
     { inherit langC langCC langObjC langObjCpp langAda langFortran langVhdl langGo version; isGNU = true; };
diff --git a/pkgs/development/compilers/gcc/7/default.nix b/pkgs/development/compilers/gcc/7/default.nix
index 48b245c1006f5..032a20271ee05 100644
--- a/pkgs/development/compilers/gcc/7/default.nix
+++ b/pkgs/development/compilers/gcc/7/default.nix
@@ -35,6 +35,7 @@
 , darwin ? null
 , flex ? null
 , buildPlatform, hostPlatform, targetPlatform
+, buildPackages
 }:
 
 assert langJava     -> zip != null && unzip != null
@@ -323,6 +324,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++
 
     # Basic configuration
     [
@@ -374,14 +377,6 @@ stdenv.mkDerivation ({
     # Ada
     optional langAda "--enable-libada" ++
 
-    # Cross-compilation
-    optional (targetPlatform == hostPlatform) (
-      let incDir = if hostPlatform.isDarwin
-                     then "${darwin.usr-include}"
-                     else "${getDev stdenv.cc.libc}/include";
-      in "--with-native-system-header-dir=${incDir}"
-    ) ++
-
     platformFlags ++
     optional (targetPlatform != hostPlatform) crossConfigureFlags ++
     optional (!bootstrap) "--disable-bootstrap" ++
@@ -446,12 +441,12 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, targetPlatform != hostPlatform
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
     buildFlags = "";
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
@@ -459,18 +454,21 @@ stdenv.mkDerivation ({
   # http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210
   CC = if stdenv.system == "x86_64-solaris" then "gcc -m64" else "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -481,39 +479,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${getDev libcCross}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${getDev libcCross}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru =
     { inherit langC langCC langObjC langObjCpp langAda langFortran langVhdl langGo version; isGNU = true; };
diff --git a/pkgs/development/compilers/gcc/builder.sh b/pkgs/development/compilers/gcc/builder.sh
index ee56425f00b42..d21755d7b1dcb 100644
--- a/pkgs/development/compilers/gcc/builder.sh
+++ b/pkgs/development/compilers/gcc/builder.sh
@@ -1,8 +1,12 @@
 source $stdenv/setup
 
 
-export NIX_FIXINC_DUMMY=$NIX_BUILD_TOP/dummy
-mkdir $NIX_FIXINC_DUMMY
+oldOpts="$(shopt -po nounset)" || true
+set -euo pipefail
+
+
+export NIX_FIXINC_DUMMY="$NIX_BUILD_TOP/dummy"
+mkdir "$NIX_FIXINC_DUMMY"
 
 
 if test "$staticCompiler" = "1"; then
@@ -13,141 +17,125 @@ fi
 
 
 # GCC interprets empty paths as ".", which we don't want.
-if test -z "$CPATH"; then unset CPATH; fi
-if test -z "$LIBRARY_PATH"; then unset LIBRARY_PATH; fi
-echo "\$CPATH is \`$CPATH'"
-echo "\$LIBRARY_PATH is \`$LIBRARY_PATH'"
+if test -z "${CPATH-}"; then unset CPATH; fi
+if test -z "${LIBRARY_PATH-}"; then unset LIBRARY_PATH; fi
+echo "\$CPATH is \`${CPATH-}'"
+echo "\$LIBRARY_PATH is \`${LIBRARY_PATH-}'"
 
 if test "$noSysDirs" = "1"; then
 
-    if test -e $NIX_CC/nix-support/orig-libc; then
-
-        # Figure out what extra flags to pass to the gcc compilers
-        # being generated to make sure that they use our glibc.
-        extraFlags="$(cat $NIX_CC/nix-support/libc-cflags)"
-        extraLDFlags="$(cat $NIX_CC/nix-support/libc-ldflags) $(cat $NIX_CC/nix-support/libc-ldflags-before || true)"
+    declare \
+        EXTRA_BUILD_FLAGS EXTRA_FLAGS EXTRA_TARGET_FLAGS \
+        EXTRA_BUILD_LDFLAGS EXTRA_TARGET_LDFLAGS
 
-        # Use *real* header files, otherwise a limits.h is generated
-        # that does not include Glibc's limits.h (notably missing
-        # SSIZE_MAX, which breaks the build).
-        export NIX_FIXINC_DUMMY=$libc_dev/include
-
-        # The path to the Glibc binaries such as `crti.o'.
-        glibc_libdir="$(cat $NIX_CC/nix-support/orig-libc)/lib"
-
-    else
-        # Hack: support impure environments.
-        extraFlags="-isystem /usr/include"
-        extraLDFlags="-L/usr/lib64 -L/usr/lib"
-        glibc_libdir="/usr/lib"
-        export NIX_FIXINC_DUMMY=/usr/include
-    fi
+    for pre in 'BUILD_' ''; do
+        curCC="NIX_${pre}CC"
+        curFIXINC="NIX_${pre}FIXINC_DUMMY"
 
-    extraFlags="-I$NIX_FIXINC_DUMMY $extraFlags"
-    extraLDFlags="-L$glibc_libdir -rpath $glibc_libdir $extraLDFlags"
+        declare -a extraFlags=() extraLDFlags=()
+        if [[ -e "${!curCC}/nix-support/orig-libc" ]]; then
+            # Figure out what extra flags to pass to the gcc compilers being
+            # generated to make sure that they use our glibc.
+            extraFlags=($(cat "${!curCC}/nix-support/libc-cflags"))
+            extraLDFlags=($(cat "${!curCC}/nix-support/libc-ldflags") $(cat "${!curCC}/nix-support/libc-ldflags-before" || true))
 
-    # BOOT_CFLAGS defaults to `-g -O2'; since we override it below,
-    # make sure to explictly add them so that files compiled with the
-    # bootstrap compiler are optimized and (optionally) contain
-    # debugging information (info "(gccinstall) Building").
-    if test -n "$dontStrip"; then
-        extraFlags="-O2 -g $extraFlags"
-    else
-        # Don't pass `-g' at all; this saves space while building.
-        extraFlags="-O2 $extraFlags"
-    fi
+            # The path to the Glibc binaries such as `crti.o'.
+            glibc_libdir="$(cat "${!curCC}/nix-support/orig-libc")/lib"
+            glibc_devdir="$(cat "${!curCC}/nix-support/orig-libc-dev")"
 
-    EXTRA_FLAGS="$extraFlags"
-    for i in $extraLDFlags; do
-        EXTRA_LDFLAGS="$EXTRA_LDFLAGS -Wl,$i"
-    done
+            # Use *real* header files, otherwise a limits.h is generated that
+            # does not include Glibc's limits.h (notably missing SSIZE_MAX,
+            # which breaks the build).
+            declare NIX_${pre}FIXINC_DUMMY="$glibc_devdir/include"
+        else
+            # Hack: support impure environments.
+            extraFlags=("-isystem" "/usr/include")
+            extraLDFlags=("-L/usr/lib64" "-L/usr/lib")
+            glibc_libdir="/usr/lib"
+            declare NIX_${pre}FIXINC_DUMMY=/usr/include
+        fi
 
-    if test -n "$targetConfig"; then
-        # Cross-compiling, we need gcc not to read ./specs in order to build
-        # the g++ compiler (after the specs for the cross-gcc are created).
-        # Having LIBRARY_PATH= makes gcc read the specs from ., and the build
-        # breaks. Having this variable comes from the default.nix code to bring
-        # gcj in.
-        unset LIBRARY_PATH
-        unset CPATH
-    else
-        if test -z "$NIX_CC_CROSS"; then
-            EXTRA_TARGET_CFLAGS="$EXTRA_FLAGS"
-            EXTRA_TARGET_CXXFLAGS="$EXTRA_FLAGS"
-            EXTRA_TARGET_LDFLAGS="$EXTRA_LDFLAGS"
+        extraFlags=("-I${!curFIXINC}"
+                    "${extraFlags[@]}")
+        extraLDFlags=("-L$glibc_libdir" "-rpath" "$glibc_libdir"
+                      "${extraLDFlags[@]}")
+
+        # BOOT_CFLAGS defaults to `-g -O2'; since we override it below, make
+        # sure to explictly add them so that files compiled with the bootstrap
+        # compiler are optimized and (optionally) contain debugging information
+        # (info "(gccinstall) Building").
+        if test -n "${dontStrip-}"; then
+            extraFlags=("-O2" "-g" "${extraFlags[@]}")
         else
-            # This the case of cross-building the gcc.
-            # We need special flags for the target, different than those of the build
-            # Assertion:
-            test -e $NIX_CC_CROSS/nix-support/orig-libc
+            # Don't pass `-g' at all; this saves space while building.
+            extraFlags=("-O2" "${extraFlags[@]}")
+        fi
 
-            # Figure out what extra flags to pass to the gcc compilers
-            # being generated to make sure that they use our glibc.
-            extraFlags="$(cat $NIX_CC_CROSS/nix-support/libc-cflags)"
-            extraLDFlags="$(cat $NIX_CC_CROSS/nix-support/libc-ldflags) $(cat $NIX_CC_CROSS/nix-support/libc-ldflags-before)"
+        declare EXTRA_${pre}FLAGS="${extraFlags[*]}"
+        for i in "${extraLDFlags[@]}"; do
+            declare EXTRA_${pre}LDFLAGS+=" -Wl,$i"
+        done
+    done
 
-            # The path to the Glibc binaries such as `crti.o'.
-            glibc_dir="$(cat $NIX_CC_CROSS/nix-support/orig-libc)"
-            glibc_libdir="$glibc_dir/lib"
-            glibc_devdir="$(cat $NIX_CC_CROSS/nix-support/orig-libc-dev)"
-            configureFlags="$configureFlags --with-native-system-header-dir=$glibc_devdir/include"
-
-            # Use *real* header files, otherwise a limits.h is generated
-            # that does not include Glibc's limits.h (notably missing
-            # SSIZE_MAX, which breaks the build).
-            NIX_FIXINC_DUMMY_CROSS="$glibc_devdir/include"
-
-            extraFlags="-I$NIX_FIXINC_DUMMY_CROSS $extraFlags"
-            extraLDFlags="-L$glibc_libdir -rpath $glibc_libdir $extraLDFlags"
-
-            EXTRA_TARGET_CFLAGS="$extraFlags"
-            for i in $extraLDFlags; do
-                EXTRA_TARGET_LDFLAGS="$EXTRA_TARGET_LDFLAGS -Wl,$i"
-            done
-        fi
+    if test -z "${targetConfig-}"; then
+        # host = target, so the flags are the same
+        EXTRA_TARGET_FLAGS="$EXTRA_FLAGS"
+        EXTRA_TARGET_LDFLAGS="$EXTRA_LDFLAGS"
     fi
 
     # CFLAGS_FOR_TARGET are needed for the libstdc++ configure script to find
     # the startfiles.
     # FLAGS_FOR_TARGET are needed for the target libraries to receive the -Bxxx
     # for the startfiles.
-    makeFlagsArray+=( \
-        NATIVE_SYSTEM_HEADER_DIR="$NIX_FIXINC_DUMMY" \
-        SYSTEM_HEADER_DIR="$NIX_FIXINC_DUMMY" \
-        CFLAGS_FOR_BUILD="$EXTRA_FLAGS $EXTRA_LDFLAGS" \
-        CXXFLAGS_FOR_BUILD="$EXTRA_FLAGS $EXTRA_LDFLAGS" \
-        CFLAGS_FOR_TARGET="$EXTRA_TARGET_CFLAGS $EXTRA_TARGET_LDFLAGS" \
-        CXXFLAGS_FOR_TARGET="$EXTRA_TARGET_CFLAGS $EXTRA_TARGET_LDFLAGS" \
-        FLAGS_FOR_TARGET="$EXTRA_TARGET_CFLAGS $EXTRA_TARGET_LDFLAGS" \
-        LDFLAGS_FOR_BUILD="$EXTRA_FLAGS $EXTRA_LDFLAGS" \
-        LDFLAGS_FOR_TARGET="$EXTRA_TARGET_LDFLAGS $EXTRA_TARGET_LDFLAGS" \
+    makeFlagsArray+=(
+        "BUILD_SYSTEM_HEADER_DIR=$NIX_BUILD_FIXINC_DUMMY"
+        "SYSTEM_HEADER_DIR=$NIX_BUILD_FIXINC_DUMMY"
+        "NATIVE_SYSTEM_HEADER_DIR=$NIX_FIXINC_DUMMY"
+
+        "LDFLAGS_FOR_BUILD=$EXTRA_BUILD_LDFLAGS"
+        #"LDFLAGS=$EXTRA_LDFLAGS"
+        "LDFLAGS_FOR_TARGET=$EXTRA_TARGET_LDFLAGS"
+
+        "CFLAGS_FOR_BUILD=$EXTRA_BUILD_FLAGS $EXTRA_BUILD_LDFLAGS"
+        "CXXFLAGS_FOR_BUILD=$EXTRA_BUILD_FLAGS $EXTRA_BUILD_LDFLAGS"
+        "FLAGS_FOR_BUILD=$EXTRA_BUILD_FLAGS $EXTRA_BUILD_LDFLAGS"
+
+        # It seems there is a bug in GCC 5
+        #"CFLAGS=$EXTRA_FLAGS $EXTRA_LDFLAGS"
+        #"CXXFLAGS=$EXTRA_FLAGS $EXTRA_LDFLAGS"
+
+        "CFLAGS_FOR_TARGET=$EXTRA_TARGET_FLAGS $EXTRA_TARGET_LDFLAGS"
+        "CXXFLAGS_FOR_TARGET=$EXTRA_TARGET_FLAGS $EXTRA_TARGET_LDFLAGS"
+        "FLAGS_FOR_TARGET=$EXTRA_TARGET_FLAGS $EXTRA_TARGET_LDFLAGS"
+    )
+
+    if test -z "${targetConfig-}"; then
+        makeFlagsArray+=(
+            "BOOT_CFLAGS=$EXTRA_FLAGS $EXTRA_LDFLAGS"
+            "BOOT_LDFLAGS=$EXTRA_TARGET_FLAGS $EXTRA_TARGET_LDFLAGS"
         )
-
-    if test -z "$targetConfig"; then
-        makeFlagsArray+=( \
-            BOOT_CFLAGS="$EXTRA_FLAGS $EXTRA_LDFLAGS" \
-            BOOT_LDFLAGS="$EXTRA_TARGET_CFLAGS $EXTRA_TARGET_LDFLAGS" \
-            )
     fi
 
-    if test -n "$targetConfig" -a "$crossStageStatic" == 1; then
+    if test -n "${targetConfig-}" -a "$crossStageStatic" == 1; then
         # We don't want the gcc build to assume there will be a libc providing
         # limits.h in this stagae
-        makeFlagsArray+=( \
-            LIMITS_H_TEST=false \
-            )
+        makeFlagsArray+=(
+            'LIMITS_H_TEST=false'
+        )
     else
-        makeFlagsArray+=( \
-            LIMITS_H_TEST=true \
-            )
+        makeFlagsArray+=(
+            'LIMITS_H_TEST=true'
+        )
     fi
 fi
 
-if test -n "$targetConfig"; then
+if test -n "${targetConfig-}"; then
     # The host strip will destroy some important details of the objects
     dontStrip=1
 fi
 
+eval "$oldOpts"
+
 providedPreConfigure="$preConfigure";
 preConfigure() {
     if test -n "$newlibSrc"; then
diff --git a/pkgs/development/compilers/gcc/snapshot/default.nix b/pkgs/development/compilers/gcc/snapshot/default.nix
index 981ac44d1b19f..f2f8eeb09a5ec 100644
--- a/pkgs/development/compilers/gcc/snapshot/default.nix
+++ b/pkgs/development/compilers/gcc/snapshot/default.nix
@@ -35,6 +35,7 @@
 , darwin ? null
 , flex ? null
 , buildPlatform, hostPlatform, targetPlatform
+, buildPackages
 }:
 
 assert langJava     -> zip != null && unzip != null
@@ -310,6 +311,8 @@ stdenv.mkDerivation ({
       "--with-mpc=${libmpc}"
     ] ++
     optional (libelf != null) "--with-libelf=${libelf}" ++
+    optional (!(crossMingw && crossStageStatic))
+      "--with-native-system-header-dir=${getDev stdenv.cc.libc}/include" ++
 
     # Basic configuration
     [
@@ -361,14 +364,6 @@ stdenv.mkDerivation ({
     # Ada
     optional langAda "--enable-libada" ++
 
-    # Cross-compilation
-    optional (targetPlatform == hostPlatform) (
-      let incDir = if hostPlatform.isDarwin
-                     then "${darwin.usr-include}"
-                     else "${getDev stdenv.cc.libc}/include";
-      in "--with-native-system-header-dir=${incDir}"
-    ) ++
-
     platformFlags ++
     optional (targetPlatform != hostPlatform) crossConfigureFlags ++
     optional (!bootstrap) "--disable-bootstrap" ++
@@ -433,12 +428,12 @@ stdenv.mkDerivation ({
     STRIP_FOR_TARGET = "${targetPlatform.config}-strip";
     CC_FOR_TARGET = "${targetPlatform.config}-gcc";
     CXX_FOR_TARGET = "${targetPlatform.config}-g++";
-    # If we are making a cross compiler, targetPlatform != hostPlatform
-    NIX_CC_CROSS = optionalString (targetPlatform == hostPlatform) builtins.toString stdenv.cc;
+
     dontStrip = true;
     buildFlags = "";
   };
 
+  NIX_BUILD_CC = buildPackages.stdenv.cc;
 
   # Needed for the cross compilation to work
   AR = "ar";
@@ -446,18 +441,21 @@ stdenv.mkDerivation ({
   # http://gcc.gnu.org/install/specific.html#x86-64-x-solaris210
   CC = if stdenv.system == "x86_64-solaris" then "gcc -m64" else "gcc";
 
-  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find
-  # the library headers and binaries, regarless of the language being
-  # compiled.
-
-  # Note: When building the Java AWT GTK+ peer, the build system doesn't
-  # honor `--with-gmp' et al., e.g., when building
-  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just
-  # add them to $CPATH and $LIBRARY_PATH in this case.
+  # Setting $CPATH and $LIBRARY_PATH to make sure both `gcc' and `xgcc' find the
+  # library headers and binaries, regarless of the language being compiled.
+  #
+  # Note: When building the Java AWT GTK+ peer, the build system doesn't honor
+  # `--with-gmp' et al., e.g., when building
+  # `libjava/classpath/native/jni/java-math/gnu_java_math_GMP.c', so we just add
+  # them to $CPATH and $LIBRARY_PATH in this case.
   #
   # Likewise, the LTO code doesn't find zlib.
+  #
+  # Cross-compiling, we need gcc not to read ./specs in order to build the g++
+  # compiler (after the specs for the cross-gcc are created). Having
+  # LIBRARY_PATH= makes gcc read the specs from ., and the build breaks.
 
-  CPATH = makeSearchPathOutput "dev" "include" ([]
+  CPATH = optionals (targetPlatform == hostPlatform) (makeSearchPathOutput "dev" "include" ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
@@ -468,39 +466,38 @@ stdenv.mkDerivation ({
     # On GNU/Hurd glibc refers to Mach & Hurd
     # headers.
     ++ optionals (libcCross != null && libcCross ? propagatedBuildInputs)
-                 libcCross.propagatedBuildInputs);
+                 libcCross.propagatedBuildInputs
+  ));
 
-  LIBRARY_PATH = makeLibraryPath ([]
+  LIBRARY_PATH = optionals (targetPlatform == hostPlatform) (makeLibraryPath ([]
     ++ optional (zlib != null) zlib
     ++ optional langJava boehmgc
     ++ optionals javaAwtGtk xlibs
     ++ optionals javaAwtGtk [ gmp mpfr ]
-    ++ optional (libpthread != null) libpthread);
-
-  EXTRA_TARGET_CFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-idirafter ${getDev libcCross}/include"
-      ]
-      ++ optionals (! crossStageStatic) [
-        "-B${libcCross.out}/lib"
-      ]
-    else null;
-
-  EXTRA_TARGET_LDFLAGS =
-    if targetPlatform != hostPlatform && libcCross != null then [
-        "-Wl,-L${libcCross.out}/lib"
-      ]
-      ++ (if crossStageStatic then [
+    ++ optional (libpthread != null) libpthread)
+  );
+
+  EXTRA_TARGET_FLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-idirafter ${getDev libcCross}/include"
+    ] ++ optionals (! crossStageStatic) [
+      "-B${libcCross.out}/lib"
+    ]);
+
+  EXTRA_TARGET_LDFLAGS = optionals
+    (targetPlatform != hostPlatform && libcCross != null)
+    ([
+      "-Wl,-L${libcCross.out}/lib"
+    ] ++ (if crossStageStatic then [
         "-B${libcCross.out}/lib"
       ] else [
         "-Wl,-rpath,${libcCross.out}/lib"
         "-Wl,-rpath-link,${libcCross.out}/lib"
-      ])
-      ++ optionals (libpthreadCross != null) [
-        "-L${libpthreadCross}/lib"
-        "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
-      ]
-    else null;
+    ]) ++ optionals (libpthreadCross != null) [
+      "-L${libpthreadCross}/lib"
+      "-Wl,${libpthreadCross.TARGET_LDFLAGS}"
+    ]);
 
   passthru =
     { inherit langC langCC langObjC langObjCpp langAda langFortran langVhdl langGo version; isGNU = true; };