dgen-sdl: fix darwin build

Disables sdltest, because it times out on hydra.

pkgs/by-name/dg/dgen-sdl/package.nix

@@ -20,6 +20,7 @@ stdenv.mkDerivation rec {
   ];
 
   configureFlags = [
+    (lib.enableFeature (!stdenv.hostPlatform.isDarwin) "sdltest")
     "--enable-debug-vdp"
     "--enable-debugger"
     "--enable-joystick"
@@ -34,6 +35,8 @@ stdenv.mkDerivation rec {
     "--with-star=no" # Needs ASM support
   ];
 
+  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.cc.isClang "-Wno-reserved-user-defined-literal";
+
   meta = with lib; {
     homepage = "https://dgen.sourceforge.net/";
     description = "Sega Genesis/Mega Drive emulator";