xlibs: replace occurrences by xorg

This seems to have been confusing people, using both xlibs and xorg, etc.
- Avoided renaming local (and different) xlibs binding in gcc*.
- Fixed cases where both xorg and xlibs were used.
Hopefully everything still works as before.

pkgs/development/libraries/directfb/default.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchurl, pkgconfig, perl, zlib, libjpeg, freetype, libpng, giflib
-, enableX11 ? true, xlibs
+, enableX11 ? true, xorg
 , enableSDL ? true, SDL }:
 
 let s = 
@@ -20,7 +20,7 @@ stdenv.mkDerivation {
 
   buildInputs = [ pkgconfig zlib libjpeg freetype giflib libpng ]
     ++ stdenv.lib.optional enableSDL SDL
-    ++ stdenv.lib.optionals enableX11 (with xlibs; [
+    ++ stdenv.lib.optionals enableX11 (with xorg; [
       xproto libX11 libXext #xextproto
       #renderproto libXrender
     ]);