Avoid atomicops, use std::atomic instead.

R=ishell@chromium.org

Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Bug: v8:8834, v8:8926
Change-Id: I07bc7bbe079fc4a138feb4d8fda91eb57046846d
Reviewed-on: https://chromium-review.googlesource.com/c/1491609Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59949}