It's now set by default if is_msan is set.

Bug: v8:9715
Change-Id: I84e05ff9a495b666292891a12a3ebe485e4a768a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1810558
Auto-Submit: Nico Weber <thakis@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63887}