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

···
     maintainers = [ ];
 
     platforms = stdenv.lib.platforms.unix;
+
+    hydraPlatforms = stdenv.lib.platforms.linux; # sdl-config times out on darwin
   };
 }

pkgs/games/freeciv/default.nix

···
 
     maintainers = with maintainers; [ pierron ];
     platforms = platforms.unix;
+    hydraPlatforms = stdenv.lib.platforms.linux; # sdl-config times out on darwin
   };
 }

pkgs/games/freedink/default.nix

···
 
     maintainers = [ stdenv.lib.maintainers.bjg ];
     platforms = stdenv.lib.platforms.all;
+    hydraPlatforms = stdenv.lib.platforms.linux; # sdl-config times out on darwin
   };
 }

pkgs/games/lbreakout2/default.nix

···
     license = licenses.gpl2;
     maintainers = [ maintainers.ciil ];
     platforms = platforms.unix;
+    hydraPlatforms = stdenv.lib.platforms.linux; # sdl-config times out on darwin
   };
 }