The dispatch_semaphore_t is a higher-level, more-efficient semaphore
primitive if the cross-process capabilities of semaphore_t are not
needed.

Bug: chromium:1012386
Change-Id: I9cc6f025f00159f9424c054a3395542b9db00b89
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1848211Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Robert Sesek <rsesek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64254}