Both fields are accessed during background compilation and thus need
to be written atomically.

This CL changes the default setters `set_foo(value, mode)` to use
relaxed stores underneath.

Bug: v8:7790
Change-Id: I49161a548cb0ef6797bd3e5592dc5bf0c9a27a15
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2704076Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72899}