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/applications/misc/xcruiser/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, gccmakedep, xlibs }:
+{ stdenv, fetchurl, gccmakedep, xorg }:
 
 stdenv.mkDerivation {
   name = "xcruiser-0.30";
@@ -8,7 +8,7 @@ stdenv.mkDerivation {
       sha256 = "1r8whva38xizqdh7jmn6wcmfmsndc67pkw22wzfzr6rq0vf6hywi";
     };
 
-  buildInputs = with xlibs; [ gccmakedep imake libXt libXaw libXpm libXext ];
+  buildInputs = with xorg; [ gccmakedep imake libXt libXaw libXpm libXext ];
 
   configurePhase = "xmkmf -a";