Instead of using our own atomic utils, use std::atomic.

R=mstarzinger@chromium.org

Bug: v8:8916, v8:8834
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Change-Id: I663d7f28dbaaa476a62407cf42dca1927c69f68b
Reviewed-on: https://chromium-review.googlesource.com/c/1491631
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59913}