libxkbfile: patch for clang36

pkgs/servers/x11/xorg/libxkbfile-clang36.patch

@@ -0,0 +1,11 @@
+--- libxkbfile-1.0.8/src/cout.c	2012-03-07 20:37:23.000000000 -0800
++++ libxkbfile-1.0.8/src/cout.c	2015-03-24 20:51:11.000000000 -0700
+@@ -45,7 +45,7 @@
+ {
+ register int i,nOut;
+ 
+-    if ((!xkb)||(!xkb->names)||(!xkb->names->vmods))
++    if ((!xkb)||(!xkb->names))
+ 	return False;
+     for (i=nOut=0;i<XkbNumVirtualMods;i++) {
+ 	if (xkb->names->vmods[i]!=None) {

pkgs/servers/x11/xorg/overrides.nix

@@ -79,6 +79,10 @@ in
     nativeBuildInputs = [ args.python ];
   };
 
+  libxkbfile = attrs: attrs // {
+    patches = lib.optional (stdenv.cc.cc.isClang or false) ./libxkbfile-clang36.patch;
+  };
+
   libpciaccess = attrs : attrs // {
     patches = [ ./libpciaccess-apple.patch ];
   };