gtkpod: add -fcommon workaround

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

    ld: .libs/autodetection.o:/build/gtkpod-2.1.5/libgtkpod/gtkpod_app_iface.h:248: multiple definition of
      `gtkpod_app'; .libs/gtkpod_app_iface.o:/build/gtkpod-2.1.5/libgtkpod/gtkpod_app_iface.h:248: first defined here

pkgs/applications/audio/gtkpod/default.nix

@@ -11,6 +11,9 @@ stdenv.mkDerivation rec {
     url = "mirror://sourceforge/gtkpod/${pname}-${version}.tar.gz";
     sha256 = "0xisrpx069f7bjkyc8vqxb4k0480jmx1wscqxr6cpq1qj6pchzd5";
   };
+  postPatch = ''
+    sed -i 's/which/type -P/' scripts/*.sh
+  '';
 
   nativeBuildInputs = [ pkg-config wrapGAppsHook intltool ];
   buildInputs = [
@@ -19,15 +22,17 @@ stdenv.mkDerivation rec {
     gdl gnome.adwaita-icon-theme gnome.anjuta
   ] ++ (with perlPackages; [ perl XMLParser ]);
 
-  patchPhase = ''
-    sed -i 's/which/type -P/' scripts/*.sh
-  '';
+  # Workaround build failure on -fno-common toolchains like upstream
+  # gcc-10. Otherwise build fails as:
+  #   ld: .libs/autodetection.o:/build/gtkpod-2.1.5/libgtkpod/gtkpod_app_iface.h:248: multiple definition of
+  #       `gtkpod_app'; .libs/gtkpod_app_iface.o:/build/gtkpod-2.1.5/libgtkpod/gtkpod_app_iface.h:248: first defined here
+  NIX_CFLAGS_COMPILE = "-fcommon";
 
   enableParallelBuilding = true;
 
   meta = with lib; {
     description = "GTK Manager for an Apple ipod";
-    homepage = "http://gtkpod.sourceforge.net";
+    homepage = "https://sourceforge.net/projects/gtkpod/";
     license = licenses.gpl2Plus;
     platforms = platforms.linux;
     maintainers = [ maintainers.skeidel ];