uae: add -fcommon workaround

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

    ld: bsdsocket.o:(.bss+0x0): multiple definition of
      `socketbases'; main.o:(.bss+0x2792c0): first defined here

pkgs/applications/emulators/uae/default.nix

@@ -15,6 +15,10 @@ stdenv.mkDerivation rec {
   buildInputs = [ gtk2 alsa-lib SDL ];
 
   hardeningDisable = [ "format" ];
+  # Workaround build failure on -fno-common toolchains:
+  #   ld: bsdsocket.o:(.bss+0x0): multiple definition of
+  #     `socketbases'; main.o:(.bss+0x2792c0): first defined here
+  NIX_CFLAGS_COMPILE = "-fcommon";
   LDFLAGS = [ "-lm" ];
 
   meta = {