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

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

After a look at preliminary results from commit 88cf37d2a86d5b66,
I realized it'd be a good idea to spew out the maximum depth measurement
seen by check_stack_depth.  So add some quick-n-dirty code to do that.
Like the previous commit, this will be reverted once we've gathered
a set of buildfarm runs with it.