[Simh] Unable to build on NetBSD

[Bailey, Scott]

I don't know if this comment represents scope creep or not, but I recently browsed the
VAX MP Technical Overview:

http://www.oboguev.net/vax_mp/VAX%20MP%20Technical%20Overview.pdf

and it has an eye-opening dissection of the pitfalls associated with threaded emulation
when the memory consistency model of the emulated hardware is not the same as
the host hardware.

It's easy to spout off from the back seat :-) but it seems like we collectively would want
to give serious thought to any general simh API that might wander into this territory so
it is possible to guarantee correctness (while hopefully not punishing performance any
more than is necessary).

Regards,
Scott