x86/string: correct memmove()'s forwarding to memcpy()

With memcpy() expanding to the compiler builtin, we may not hand it
overlapping source and destination. We strictly mean to forward to our
own implementation (a few lines up in the same source file).

Fixes: 78825e1c60 ("x86/string: Clean up x86/string.h")
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 7b93d92a35
master date: 2021-02-04 13:59:56 +0100

xen/arch/x86/string.c

@@ -43,7 +43,8 @@ void *(memmove)(void *dest, const void *src, size_t n)
         return dest;
 
     if ( dest < src )
-        return memcpy(dest, src, n);
+        /* Depends on Xen's implementation operating forwards. */
+        return (memcpy)(dest, src, n);
 
     asm volatile (
         "   std         ; "