@Victor, I set up a FreeBSD 12.0 VM (in Hyper-v) and made sure core files were getting generated for segfaults. Then I cloned the cpython repo, built it (using GCC), and ran regrtest as you recommended. It generated no core files after half an hour. I adjusted the VM down to 1 CPU from 4 and there were no segfaults over an hour and a half of running those 4 test loops. So I've set the VM to 10% of a CPU and still have gotten no core files after over half an hour. The load average has been hovering between 5 and 6. I guess I'm not starving the VM enough. :)
Any ideas of how far I need to throttle the VM? Is there more than just CPU that I need to limit?