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

docs/README.md

@@ -51,6 +51,7 @@ More documentation and FAQs are available online at [the wiki](http://wiki.libsd
 - [Windows](README-windows.md)
 - [WinRT](README-winrt.md)
 - [PSVita](README-vita.md)
+- [Nokia N-Gage](README-ngage.md)
 
 If you need help with the library, or just want to discuss SDL related
 issues, you can join the [SDL Discourse](https://discourse.libsdl.org/),