LWP private support / TLS support

Hi all,
I've just committed the first major step to TLS support on NetBSD.
The HPPA part is not complete at the moment. I'm not sure if CR27 is
correctly updated during context switches in all cases. There is also
the problem that the first lwp_setprivate call (during libpthread init)
seems to get garbled. If both issues are fixed, the #if 0 around
__HAVE___LWP_GETPRIVATE_FAST in machine/types.h can be removed and after
a rebuild of libpthread, the ATF test cases for it should still work.

Joerg