x86_64: Always use builtin memcpy on gcc 4.3

Jan asked to always use the builtin memcpy on gcc 4.3 mainline because
it should generate better code than the old macro. Let's try it.

Cc: Jan Hubicka <jh@suse.cz>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-x86_64/string.h

@@ -29,6 +29,9 @@ return (to);
    function. */
 
 #define __HAVE_ARCH_MEMCPY 1
+#if (__GNUC__ == 4 && __GNUC_MINOR__ >= 3) || __GNUC__ > 4
+extern void *memcpy(void *to, const void *from, size_t len);
+#else
 extern void *__memcpy(void *to, const void *from, size_t len); 
 #define memcpy(dst,src,len) \
 	({ size_t __len = (len);				\
@@ -38,7 +41,7 @@ extern void *__memcpy(void *to, const void *from, size_t len);
 	   else							\
 		 __ret = __builtin_memcpy((dst),(src),__len);	\
 	   __ret; }) 
-
+#endif
 
 #define __HAVE_ARCH_MEMSET
 void *memset(void *s, int c, size_t n);