libthread_xu - Remove unconditional debugging, slight code flow adjustment

* Remove an unconditional fprintf to stderr that is no longer needed

* Ensure that __thr_umtx_timedlock() doesn't break out on EINTR.  Note
  however that the functions it calls shouldn't be able to return EINTR
  so this change is really just to make things look more correct.
cpdup - native linux compile

* Add an #ifdef to define away __ specials so a straight build under
  linux works on unmodified sources.