This PR fixes a potential race condition in
https://github.com/llvm/llvm-project/pull/90930.
This race can happen because the original code set `m_info->m_isAlive =
true` **after** the timer thread is created. So if there is a context
switch happens and timer thread checks `m_info->m_isAlive` before main
thread got a chance to run `m_info->m_isAlive = true`, the timer thread
may treat `ThreadPlanSingleThreadTimeout` as not alive and simply exit
resulting in async interrupt never being sent to resume all threads
(deadlock).
The PR fixes the race by initializing all states **before** worker timer
thread creates.
Co-authored-by: jeffreytan81 <jeffreytan@fb.com>
54154f9f06