qt4: maintenance update 4.8.4 -> 4.8.5

Also fixed search path for libGL.
Tested building against master.

pkgs/development/libraries/mesa/default.nix

@@ -137,7 +137,7 @@ stdenv.mkDerivation {
   '';
   #ToDo: @vcunat isn't sure if drirc will be found when in $out/etc/, but it doesn't seem important ATM
 
-  passthru = { inherit libdrm; inherit version; };
+  passthru = { inherit libdrm version driverLink; };
 
   meta = {
     description = "An open source implementation of OpenGL";