treewide: disable sdl-config darwin time outs

sdl-config has an issue on hydra where it will hang when run on
Darwin. This is probably related to the headless mode that is set up &
the sdl-config program waiting for a graphical to finish.

pkgs/games/ball-and-paddle/default.nix

@@ -38,5 +38,7 @@ stdenv.mkDerivation rec {
     maintainers = [ ];
 
     platforms = stdenv.lib.platforms.unix;
+
+    hydraPlatforms = stdenv.lib.platforms.linux; # sdl-config times out on darwin
   };
 }