Forced GCs are used in testing configurations and under memory
pressure. Use atomic sweeping for C++ in those scenarios as testing
GCs require that destructors are immediately invoked after the GC
call.

Bug: chromium:1056170
Change-Id: I03c13fa7a30cf74076807834c5e6d0c1fe52bb87
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2704543
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72873}