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/audio/rkrlv2/default.nix

@@ -1,5 +1,5 @@
 { stdenv, pkgs, fetchFromGitHub,
-automake, pkgconfig, lv2, fftw, cmake, xlibs, libjack2, libsamplerate, libsndfile
+automake, pkgconfig, lv2, fftw, cmake, xorg, libjack2, libsamplerate, libsndfile
 }:
 
 stdenv.mkDerivation rec {
@@ -13,7 +13,7 @@ stdenv.mkDerivation rec {
     sha256 = "0kr3rvq7n1bh47qryyarcpiibms601qd8l1vypmm61969l4d4bn8";
   };
 
-  buildInputs = with xlibs; [ automake pkgconfig lv2 fftw cmake libXpm libjack2 libsamplerate libsndfile libXft ];
+  buildInputs = with xorg; [ automake pkgconfig lv2 fftw cmake libXpm libjack2 libsamplerate libsndfile libXft ];
 
   meta = {
     description = "Rakarrak effects ported to LV2";