sysutils/e2fsprogs: Try and enable backtrace() where possible.

The configure script doesn't find backtrace() because it does not
attempt linking against -lexecinfo -lelf.

Note that currently backtrace() is broken at least on 12.1 amd64, and
does not return any frames. Filed separately as
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=243746

PR: 242798 (which prompts this change, but is not fixed)