... btw, should we drop the now-unused config/ax_prog_perl_modules.m4 ?
I'm inclined to do so, on the grounds that we're not likely ever to
need it. I doubt we'd agree to require a non-core Perl module as
part of either our build tooling or PL/Perl's dependencies. Not
to mention that it'd go away anyway if we switch to meson.
regards, tom lane