Invalid ref construction (should assume a memory fence), and invalid
unconditional use of an optional ref.

Bug: v8:7790,chromium:1236303,chromium:1236307
Change-Id: Id0a12222d3d29a0728290ad5269da0946647a5ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3070698
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76074}