xwinmosaic: pull upstream fix for -fno-common toolchains

Without the change build fails as:

$ nix build --impure --expr 'with import ./. {}; xwinmosaic.overrideAttrs (oa: { NIX_CFLAGS_COMPILE = (oa.NIX_CFLAGS_COMPILE or "") + "-fno-common"; })'
ld: CMakeFiles/xwinmosaic.dir/main.c.o:(.bss+0xc0):
multiple definition of `a_NET_CURRENT_DESKTOP'; CMakeFiles/xwinmosaic.dir/x_interaction.c.o:(.bss+0xc0): first defined here
ld: CMakeFiles/xwinmosaic.dir/main.c.o:(.bss+0xc8):
multiple definition of `a_NET_DESKTOP_VIEWPORT'; CMakeFiles/xwinmosaic.dir/x_interaction.c.o:(.bss+0xc8): first defined here

pkgs/tools/X11/xwinmosaic/default.nix

···
-{ lib, stdenv, fetchFromGitHub, gtk2, cmake, pkg-config, libXdamage }:
+{ lib, stdenv, fetchFromGitHub, fetchpatch, gtk2, cmake, pkg-config, libXdamage }:
 
 stdenv.mkDerivation rec {
   version = "0.4.2";
···
     rev = "refs/tags/v${version}";
     sha256 = "16qhrpgn84fz0q3nfvaz5sisc82zk6y7c0sbvbr69zfx5fwbs1rr";
   };
+
+  patches = [
+    # Pull upstream fix for -fno-common toolchains like upstream gcc-10:
+    #  https://github.com/soulthreads/xwinmosaic/pull/33
+    (fetchpatch {
+      name = "fno-common.patch";
+      url = "https://github.com/soulthreads/xwinmosaic/commit/a193a3f30850327066e5a93b29316cba2735e10d.patch";
+      sha256 = "0qpk802j5x6bsfvj6jqw1nz482jynwyk7yrrh4bsziwc53khm95q";
+    })
+  ];
 
   nativeBuildInputs = [ pkg-config cmake ];
   buildInputs = [ gtk2 libXdamage ];