[RFC] Improve performance of multi-threaded debugging

[Jim Blandy]

Kevin Buettner <kevinb@redhat.com> writes:
> The only fly in the ointment is that the signal based event model only
> knows about thread creation, but not about thread death.  So it won't
> catch thread death until some new thread is created.  I'm not sure
> what the implications of this are in practice.

Even in the signal-based model, we're attached to all the threads, so
we should get a wait status via lwp_pool_waitpid.  Isn't that working?