fix from upstream for the cld issue on x86

http://bugs.gentoo.org/217097

--- include/SDL_stdinc.h	(revision 3535)
+++ include/SDL_stdinc.h	(revision 3536)
@@ -373,6 +373,7 @@ do {							\
 	__asm__ __volatile__ (				\
 		"std\n\t"				\
 		"rep ; movsl\n\t"			\
+		"cld\n\t"				\
 		: "=&c" (u0), "=&D" (u1), "=&S" (u2)	\
 		: "0" (n >> 2),				\
 		  "1" (dstp+(n-4)), "2" (srcp+(n-4))	\