In particular, perl with $Config{osname} = msys should only be used if
the build target is msys (which is currently buildable but not usable).
For builds targeted at native Windows, perl from the ucrt64 toolchain is
suitable.
Discussion: https://postgr.es/m/20220216210141.5glt5isg5qtwty4c@alap3.anarazel.de
Normally "prove" and "perl" come from the same Perl installation,
but we support the case where they don't (mainly because the MSys
buildfarm animals need this). In that case, AX_PROG_PERL_MODULES
is completely the wrong thing to use, because it's checking what
"perl" has. Instead, make a little TAP test script including the
required modules, and run that under "prove".
We don't need ax_prog_perl_modules.m4 at all after this change,
so remove it.
Back-patch to all supported branches, for the buildfarm's benefit.
(In v10, this also back-patches the effects of commit 264eb03aa.)
Andrew Dunstan and Tom Lane, per an observation by Noah Misch
Discussion: https://postgr.es/m/E1moZHS-0002Cu-Ei@gemulon.postgresql.org
Tom Lane
Andrew Dunstan