wmfs: fix build on -fno-common toolchain

Without the change build fails on -fno-common tollchains as:

    $ nix build --impure --expr 'with import ~/nm {}; wmfs.override { stdenv = clang13Stdenv; }'
    ...
    ld: src/log.o:(.bss+0x0): multiple definition of `W'; src/barwin.o:(.bss+0x0): first defined here
    ld: src/wmfs.o:(.bss+0x0): multiple definition of `W'; src/barwin.o:(.bss+0x0): first defined here
    ld: src/wmfs.o:(.bss+0x10): multiple definition of `event_handle'; src/client.o:(.bss+0x10): first defined here

pkgs/applications/window-managers/wmfs/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub,
+{ lib, stdenv, fetchFromGitHub, fetchpatch,
   libX11, libXinerama, libXrandr, libXpm, libXft, imlib2 }:
 stdenv.mkDerivation {
   pname = "wmfs";
@@ -12,6 +12,17 @@ stdenv.mkDerivation {
     rev = "b7b8ff812d28c79cb22a73db2739989996fdc6c2";
   };
 
+  patches = [
+    # Pull patch pending upstream inclusion to fix build on
+    # -fno-common toolchain like upstream gcc-10:
+    #  https://github.com/xorg62/wmfs/pull/104
+    (fetchpatch {
+      name = "fno-common.patch";
+      url = "https://github.com/xorg62/wmfs/commit/e4ec12618f4689d791892ebb49df9610a25d24d3.patch";
+      sha256 = "0qvwry9sikvr85anzha9x4gcx0r2ckwdxqw2in2l6bl9z9d9c0w2";
+    })
+  ];
+
   buildInputs = [
     imlib2
     libX11