gnome_mplayer: add -fcommon workaround

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

    ld: mpris-interface.o:src/playlist.h:32: multiple definition of
      `plclose'; gui.o:src/playlist.h:32: first defined here

pkgs/applications/video/gnome-mplayer/default.nix

@@ -23,6 +23,11 @@ stdenv.mkDerivation rec {
     })
   ];
 
+  # Workaround build failure on -fno-common toolchains:
+  #   ld: mpris-interface.o:src/playlist.h:32: multiple definition of
+  #     `plclose'; gui.o:src/playlist.h:32: first defined here
+  NIX_CFLAGS_COMPILE = "-fcommon";
+
   meta = with lib; {
     description = "Gnome MPlayer, a simple GUI for MPlayer";
     homepage = "https://sites.google.com/site/kdekorte2/gnomemplayer";