Scott Bennett:
Fortunately, zstd isn't available for all platforms and architectures. So as long as we steer clear of a platform monoculture, we'll be fine. (That said, this particular bug is on BSD. But people should still run relays on BSD, so we get a good OS mix.)
Are the BSDs the only systems that have zstd available?
No, Debian has libzstd as well and produces similar stack traces.
https://packages.debian.org/stretch/libzstd1 https://lists.torproject.org/pipermail/tor-relays/2017-September/013057.html