SuspendThread fails with STATUS_THREAD_IS_TERMINATING for a thread that
has begun to exit while its handle is not signaled yet. TryDeliver took
only the signaled handle as an exit, so the raise deliverer, which keeps
sweeping a target in host code until delivery or exit, threw "cannot
suspend the target thread" and aborted the process when that target
exited in between. The suspension now reads the NTSTATUS from
NtSuspendThread and treats a terminating target as exited; other
failures still throw.
guest_raise_exiting_thread raises at 32 threads per round that block in
a host wait and exit after it, for 100 rounds.
