Add support for the Nokia N-Gage (#5597)

* Add initial support for the Nokia N-Gage

* N-Gage: disable clipping for the time being, issue needs to be resolved later

* Move va_copy definition to SDL_internal.h

* Move stdlib.h include to SDL_config_ngage.h, much cleaner this way

* Remove redundant include, add HAVE_STDLIB_H

* Revert "N-Gage: disable clipping for the time being, issue needs to be resolved later"

This reverts commit 4f5f0fc36c.

* N-Gage: fix clipping issue by providing proper math functions

include/SDL_config.h

@@ -43,6 +43,8 @@
 #include "SDL_config_os2.h"
 #elif defined(__EMSCRIPTEN__)
 #include "SDL_config_emscripten.h"
+#elif defined(__NGAGE__)
+#include "SDL_config_ngage.h"
 #else
 /* This is a minimal configuration just to get SDL running on new platforms. */
 #include "SDL_config_minimal.h"