WinRT: merged with latest SDL 2.x/HG code

SDL 2.x recently accepted patches to enable OpenGL ES 2 support via Google's ANGLE library.  The thought is to try to eventually merge SDL/WinRT's OpenGL code with SDL-official's.

include/SDL_main.h

@@ -113,7 +113,7 @@ extern "C" {
  *  Calling this yourself without knowing what you're doing can cause
  *  crashes and hard to diagnose problems with your application.
  */
-extern DECLSPEC void SDL_SetMainReady(void);
+extern DECLSPEC void SDLCALL SDL_SetMainReady(void);
 
 #ifdef __WIN32__