libthr signal bugs

I recently tried libmapping libc_r to libthr on my -current system
from Sep 10, and ran into a lot of problems with signal delivery.
Specifically, mozilla hung in the sigwait state when I opened a bunch
of tabs in quick succession, and other processes did not respond to
signals using ^C/^Z/^\, or even kill -HUP.  The problems went away
when I reverted to libc_r.

Kris