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/haskell-modules/default.nix

@@ -43,7 +43,7 @@ let
         overrideScope = f: callPackageWithScope (mkScope (fix (extend scope.__unfix__ f))) drv args;
       };
 
-      mkScope = scope: pkgs // pkgs.xlibs // pkgs.gnome // scope;
+      mkScope = scope: pkgs // pkgs.xorg // pkgs.gnome // scope;
       defaultScope = mkScope self;
       callPackage = drv: args: callPackageWithScope defaultScope drv args;