Support alternate GNU getopt binary on OpenBSD

[0xkag]

OpenBSD getopt does not support -l. There's a gnugetopt port/package that is the GNU implementation (the one on Linux) that supports -l. So if gnugetopt is present in the PATH use that, otherwise use getopt.

This is coming from https://github.com/ohmyzsh/ohmyzsh/pull/9677.

[alpha-tango-kilo]

Hey Kyle, thanks for the PR! Is this the only instance in the program that has a GNU-specific implementation do you know, or are there others we need to be careful of?

[p1r473]

Bump @0xkag