Timeouts occurred in test-concurrent-feedback-vector/CheckLoadICStates
because the main thread could enter "handshaking" mode precisely at
the moment when the worker thread successfully saw all states.
The main thread would miss this, and end up waiting forever on
a signal from the worker thread.

Bug: v8:11082
Change-Id: I0441785d908c5e27562a3620bb2195483727f118
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2519553
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70962}