vokoscreen: add -fcommon workaround

Workaround build failure on -fno-common toolchains like upstream
gcc-10. Otherwise build fails as:

    ld: alsa_device.o:(.bss+0x8): multiple definition of `rc'; QvkAlsaDevice.o:(.bss+0x8): first defined here

1 files changed, 4 insertions, 0 deletions

diff --git a/pkgs/applications/video/vokoscreen/default.nix b/pkgs/applications/video/vokoscreen/default.nix
index aeea52a4ff5a0..2bb9437f1b06f 100644
--- a/pkgs/applications/video/vokoscreen/default.nix
+++ b/pkgs/applications/video/vokoscreen/default.nix
@@ -30,6 +30,10 @@ mkDerivation rec {
     ./ffmpeg-out-of-box.patch
   ];
 
+  # Workaround build failure on -fno-common toolchains:
+  #   ld: alsa_device.o:(.bss+0x8): multiple definition of `rc'; QvkAlsaDevice.o:(.bss+0x8): first defined here
+  NIX_CFLAGS_COMPILE = "-fcommon";
+
   preConfigure = ''
     sed -i 's/lrelease-qt5/lrelease/g' vokoscreen.pro
   '';