Added annotations to help code analysis tools

CR: Bruce Dawson

include/SDL_error.h

@@ -38,7 +38,7 @@ extern "C" {
 
 /* Public functions */
 /* SDL_SetError() unconditionally returns -1. */
-extern DECLSPEC int SDLCALL SDL_SetError(const char *fmt, ...);
+extern DECLSPEC int SDLCALL SDL_SetError(SDL_PRINTF_FORMAT_STRING const char *fmt, ...) SDL_PRINTF_VARARG_FUNC(1);
 extern DECLSPEC const char *SDLCALL SDL_GetError(void);
 extern DECLSPEC void SDLCALL SDL_ClearError(void);