Instead of cmov + unconditional store, do a conditional store. At least
on Intel CPUs, this turns out to be significantly faster.

R=jkummerow@chromium.org

Bug: v8:13063
Change-Id: Ib5a89b9b9dbc88ca408a4bafc152d91407bf8d1b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3776675Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81900}