sys__lwp_create() and sys__lwp_suspend(): Only test to see if a process is
an SA process ifdef KERN_SA.

sys__sched_setaffinity(): Don't allow changing (setting) the affinity
of an SA process (or a thread in an SA process). To really set the
affinity of a thread in an SA process, we need to set the affility
for all LWPs on which that user thread will run. This really means
setting the affinity on all present and future threads on a VP
and also having the user thread always run on an lwp on that VP. The
latter needs libpthread's intervention.

(wrstuden)