x86: Fix missing __wmemcmp def for disable-multiarch build

commit 8804157a
Author: Noah Goldstein <goldstein.w.n@gmail.com>
Date:   Fri Apr 15 12:27:59 2022 -0500

    x86: Optimize memcmp SSE2 in memcmp.S

Only defined wmemcmp and missed __wmemcmp. This commit fixes that by
defining __wmemcmp and setting wmemcmp as a weak alias to __wmemcmp.

Both multiarch and disable-multiarch builds succeed and full xchecks
pass.

Reviewed-by: H.J. Lu <hjl.tools@gmail.com>