Fix watchthreads-reorder.exp fails in linux gdbserver

[Joel Brobecker]

> I've applied the patch below, to address in linux gdbserver the problem
> watchthreads-reorder.exp uncovers, similarly to how it was fixed
> in linux-nat.c.

This is a bit off topic, and even maybe a dream-that-will-never-come-true,
but I've been wondering about sharing the wait loop between GDB and gdbserver.
Sounds like a big job at the very least (in order to extract the code
from GDB for the platform currently supported), but do you think that
it's actually doable / worth the effort? It's just that we're (actually,
mostly you!) are very regularly fixing the same problem twice; once
in GDB, and then once in gdbserver. Given the complexity of this code
on some platforms, it's a real shame.

-- 
Joel