The concurrent version was added recently in crrev.com/c/3085262.

- UnusedPropertyFields requires the MapUpdater lock.
- instance_descriptors must be read atomically on the bg thread.

Finally, there appears to be a false positive report for the pattern:

 x = is_concurrent ? foo(kAcquireLoad) : foo();

Here, clang emits code that executes both the atomic and nonatomic
reads when is_concurrent is true. Needs more investigation.

Bug: v8:7790, chromium:1239009
Change-Id: I07d442e72cf0278f79f202a267e8d246f8abca1b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3090341
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76261}