Split some GTK/X11-related packages

The closure of the Pan newsreader is now down from 344 MiB to 195 MiB.

pkgs/development/libraries/atk/2.2.x.nix

@@ -8,12 +8,14 @@ stdenv.mkDerivation rec {
     sha256 = "17bkqg89l9hxbkgc76cxlin1bwczk7m6ikbccx677lrxh3kz08lb";
   };
 
+  enableParallelBuilding = true;
+
+  outputs = [ "dev" "out" "doc" ];
+
   buildNativeInputs = [ pkgconfig perl ];
 
   propagatedBuildInputs = [ glib ];
 
-  postInstall = "rm -rf $out/share/gtk-doc";
-
   meta = {
     description = "ATK, the accessibility toolkit";