[LSAN] In some glibc versions, LSan's local cache is not destroyed after a thread exits

[zhaoyujohn]

In some glibc versions, POSIX timers do not call pthread_create to spawn a thread. If memory is allocated inside such a timer, the thread's local cache is not destroyed when the thread exits, leading to a memory leak.

[zhaoyujohn]

Because timer_helper_thread is spawned via __pthread_create (instead of _pthread_create), LSan’s ThreadStartFunc isn’t invoked to set g_thread_finalize_key. thread_finalize does run, but due to g_thread_finalize_key not being set, it doesn’t produce the expected effect.