OpenBSD 5.2 and later have a proper threads implementation based on
kernel threads. Debugging support is provided through additional
ptrace(2) requests, so this diff extends the generic code in
inf-ptrace.c with OpenBSD-specific code to discover additional threads.
gdb/ChangeLog:
* obsd-nat.h: New file.
* obsd-nat.c: New file.
* Makefile.in (HFILES_NO_SRCDIR): Add obsd-nat.h.
(ALLDEPFILES): Add obsd-nat.c.