Consider reverting the autoconf 2.72 version bump requirement as it breaks compatibility with distros

[stratakis]

Bug report

Bug description:

autoconf minimum requirement was bumped to 2.72 through #115765

This breaks configure regeneration for CentOS Stream 9/RHEL9 (shipping 2.69 and extra 2.71) and CentOS Stream 10/RHEL10 (shipping 2.71). I presume other distros as well. We currently patch our spec files, lowering the version (to 2.69 and 2.71) makes them work fine.

I (re)discovered the issue by doing some testing on the newly added CentOS Stream buildbot.

And as far as I can see there is nothing used from 2.72, no functional changes. Requiring 2.72 is too aggressive and it seems it was not tested on any major distros at the time.

CPython versions tested on:

CPython main branch, 3.16, 3.15, 3.14

Operating systems tested on:

Linux

[StanFromIreland]

@terryjreedy FYI autoconf is used on all Unix systems, not just Linux. I think os-unsupported works here as it's not an issue on a supported platform.

[vstinner]

I'm not sure that we actually rely on autoconf 2.72 features, it's just the version used to regenerate configure when running regen-configure.

But AC_PREREQ([2.72]) is used configure.ac, it was changed by commit 0cafa97. Maybe we can move back to AC_PREREQ([2.71])?

If we move back to AC_PREREQ([2.71]), https://docs.python.org/dev/using/configure.html#configure-script should document that the minimum autoconf version is 2.71, but autoconf 2.72 is recommended.

cc @erlend-aasland