My plan of attack right now would be to shift the assertion logic
further back in the control flow, into osdep-unix.c's
osdep_realclock() and osdep_cpuclock(), to determine under what
conditions those functions are returning 0.

Marco: I am unable to reproduce the problem on my end. You called
this a bohrbug, so I assume you can readily reproduce the problem but
cannot determine the full set of conditions that cause it. Since you
are using a very recent SVN version of Larceny, I assume you won't
mind if I communicate source code changes to you via the repository?
Assuming that you do not mind my using that as my communication
channel, then I will set aside some time today to put such code into
the trunk's copy of osdep-unix.c (unless Will objects to such changes
being made on the trunk and would prefer I send you patches or put the
work onto a branch).

-Felix