Add some temporary code to record stack usage at server process exit.

Add some temporary code to record stack usage at server process exit.

This patch is meant to gather information from the buildfarm members, and
will be reverted in a day or so.  The idea is to try to find out the
high-water stack consumption while running the regression tests,
particularly on IA64 which is suspected to use much more stack than other
architectures.  On machines with pmap, we can use that; but the IA64 farm
members are running HPUX, so also include some bespoke code for HPUX.
(I've tested the latter on HPUX 10/HPPA; not entirely sure it will work
on HPUX 11/IA64, but we'll soon find out.)

Discussion: <CAM-w4HMwwcwaVvYcAH0_FGtG5GeXdYVRfvG81pXnSJWHnCfosQ@mail.gmail.com>