x86: Import glibc memcpy implementation

Taken from glibc version 2.14.90

--
Changes for v2:
 - None
diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h
index 3aa6c11..0ad612f 100644
--- a/arch/x86/include/asm/string.h
+++ b/arch/x86/include/asm/string.h
@@ -14,7 +14,7 @@
 #undef __HAVE_ARCH_STRCHR
 extern char * strchr(const char * s, int c);
 
-#undef __HAVE_ARCH_MEMCPY
+#define __HAVE_ARCH_MEMCPY
 extern void * memcpy(void *, const void *, __kernel_size_t);
 
 #undef __HAVE_ARCH_MEMMOVE