Allow to call clock_gettime() on the clock id for zombie process.

Reported by:	Petr Salinger <Petr.Salinger@seznam.cz>
PR:	threads/180496
Sponsored by:	The FreeBSD Foundation
There is no need to count waiters for the runningbufspace.

Sponsored by:	The FreeBSD Foundation
Assert that runningbufspace does not underflow.

Sponsored by:	The FreeBSD Foundation
Create a proper stack frame for i386 version of bcopy(), despite the
function is leaf.  The frame allows ddb to not loose the direct caller
of bcopy() in backtrace.

Other functions from support.s would benefit from the same change as
well, but for now bcopy() is the most frequent offender.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week