Ozkan Sezer
Attached three patches, so these minor os/2 bits get registered mainstream:
1. SDL_syswm.h: add SDL_SYSWM_OS2 to SDL_SYSWM_TYPE enum
2. SDL_platform.h: recognize __EMX__ too as __OS2__
3. begin_code.h: set SDLCALL as _System for OS/2.
The internal function SDL_EGL_LoadLibrary() did not delete and remove a mostly
uninitialized data structure if loading the library first failed. A later try to
use EGL then skipped initialization and assumed it was previously successful
because the data structure now already existed. This led to at least one crash
in the internal function SDL_EGL_ChooseConfig() because a NULL pointer was
dereferenced to make a call to eglBindAPI().
