googletest

Fix a race condition between the Watcher thread and the main thread
during program exit

A race condition exist between the Watcher thread and main(). A case
was found where the Watcher thread does not get execution time before
the main function returns and calls atexit(). At that point the
Watcher thread started runing tls_init() code while the main thread
was shutting down. This resulted in rare crashes and deadlocks.

Fixes #4493
Closes #4494

PiperOrigin-RevId: 621619768
Change-Id: I66f00d8f0f3c37f9937c6d13890f7fa10038256d