libX11: adds upstream patch to fix cross-compilation

With this patch applied, cross-compilation of a system image for ARM
platforms works as it did previously.

See their commit for more explanation:

 * https://cgit.freedesktop.org/xorg/lib/libX11/commit/?id=0327c427d62f671eced067c6d9b69f4e216a8cac

pkgs/servers/x11/xorg/overrides.nix

@@ -79,6 +79,13 @@ self: super:
 
   libX11 = super.libX11.overrideAttrs (attrs: {
     outputs = [ "out" "dev" "man" ];
+    patches = [
+      # Fixes an issue that happens when cross-compiling for us.
+      (fetchpatch {
+        url = "https://cgit.freedesktop.org/xorg/lib/libX11/patch/?id=0327c427d62f671eced067c6d9b69f4e216a8cac";
+        sha256 = "11k2mx56hjgw886zf1cdf2nhv7052d5rggimfshg6lq20i38vpza";
+      })
+    ];
     configureFlags = attrs.configureFlags or []
       ++ malloc0ReturnsNullCrossFlag;
     depsBuildBuild = [ buildPackages.stdenv.cc ];