Log Message:
tor: disable backtrace(3) support on netbsd-9 evbarm

backtrace(3) does not work on netbsd-9 ending up in a SIGSEGV and tor
process hanging forever (a simple way to reproduce without configuring
tor is just invoking tor via `tor --version').

Workaround for PR port-evbarm/55669.

PKGREVISION++