bsdgrep(1): Add GNU compatible version string indicator

[kevans]

Summary

mandree@ pointed out in r218614 that there's no indication
that a version of bsdgrep(1) is or is not compiled with GNU-isms. Adding
an indicator to the version string is sensible, so I've added a version
of it with "GNU compatible" in the name.

At the moment, it may or may not be 100% accurate, as it really only describes
regex compatibility. I think we're fairly close to flag/option parity as of recent
versions, so this should be a reasonable claim.

As an aside, I think I've amended the options somewhere that will likely require
an update to all of the nls/ bits, since I failed to do that.

Test Plan

Compile versions with and without GNU_GREP_COMPAT, observe grep -V