Re-enabled the O_CLOEXEC definition so config headers can be fixed

src/SDL_internal.h

@@ -51,7 +51,8 @@
 
 #include "SDL_config.h"
 
-#if !defined(O_CLOEXEC) && !defined(HAVE_O_CLOEXEC)
+/* If you run into a warning that O_CLOEXEC is redefined, update the SDL configuration header for your platform to add HAVE_O_CLOEXEC */
+#ifndef HAVE_O_CLOEXEC
 #define O_CLOEXEC                       0
 #endif