x11vnc: pull upstream fix for -fno-common toolchains

Without the change build fails on upstream gcc-10 as:

    ld: x11vnc-xwrappers.o:/build/source/src/util.h:105: multiple definition of
      `clientMutex'; x11vnc-8to24.o:/build/source/src/util.h:105: first defined here

1 files changed, 8 insertions, 0 deletions

diff --git a/pkgs/tools/X11/x11vnc/default.nix b/pkgs/tools/X11/x11vnc/default.nix
index bd10127f729f5..118ce5398c35d 100644
--- a/pkgs/tools/X11/x11vnc/default.nix
+++ b/pkgs/tools/X11/x11vnc/default.nix
@@ -19,6 +19,14 @@ stdenv.mkDerivation rec {
       url = "https://github.com/LibVNC/x11vnc/commit/69eeb9f7baa14ca03b16c9de821f9876def7a36a.patch";
       sha256 = "0hdhp32g2i5m0ihmaxkxhsn3d5f2qasadvwpgxify4xnzabmyb2d";
     })
+
+    # Pull upstream fix for -fno-common toolchains:
+    #   https://github.com/LibVNC/x11vnc/pull/121
+    (fetchpatch {
+      name = "fno-common.patch";
+      url = "https://github.com/LibVNC/x11vnc/commit/a48b0b1cd887d7f3ae67f525d7d334bd2feffe60.patch";
+      sha256 = "046gjsmg0vm0m4y9ny17y2jayc4ba7vib2whw71l5x1hjp6pksjs";
+    })
   ];
 
   nativeBuildInputs = [ autoreconfHook pkg-config ];