Thread Sanitizer reports data races on PoolHalting in THREAD, shared
between ThreadPoolProc and WaitThread. But if WaitThread reads false,
synchronization is ensured by Wait from the PoolWaitList. If it reads
true, WaitThread simply returns.
Using no_sanitize("thread") disables instrumentation for the entire
stack frame, meaning functions called within that scope are also not
checked. By using race_top in a suppression file, we can suppress
erros only when they occur at the top of the stack. This provides more
granular control over errors suppression.
As an example, this suppression addresses #2222.
