updated includes for _exit()

src/SDL.c

@@ -22,8 +22,10 @@
 
 #if defined(__WIN32__)
 #include "core/windows/SDL_windows.h"
+#elif defined(__OS2__)
+#include <stdlib.h> /* For _exit() */
 #elif !defined(__WINRT__)
-#include <unistd.h> // For _exit(), etc.
+#include <unistd.h> /* For _exit(), etc. */
 #endif
 
 #if defined(__EMSCRIPTEN__)