My code doesn't directly reference those .al files; it doesn't even directly use Term::ReadLine::Gnu (which isn't allowed anyway). All my code does is use Term::ReadLine and somehow it chooses ::Gnu (rather than ::Perl or ::Stub).

So near as I can gather, what you describe is all handled by the ::Gnu version of ReadLine.

But it doesn't seem to matter. I copied myprog.packed.pl and CLH_Utils.pm to a virginal user on a MacOS Catalina with Perl 5.18 and it ran okay, apparently falling back to Term::ReadLine::Perl.