Similar to D107799 but for *BSD (DragonFlyBSD, FreeBSD, NetBSD, OpenBSD, etc).
This Linux default has been in main and release/15.x for a while.
CMAKE_SYSTEM_PROCESSOR MATCHES "^arm" is excluded for now. It is unclear
whether the Linux arm vs armhf issue applies to *BSD.
Link: https://discourse.llvm.org/t/rfc-time-to-drop-legacy-runtime-paths/64628