Autoconf is finally getting an update after 8 years, and there are some breaking changes. A beta version has been released for testing:

https://lists.gnu.org/archive/html/autoconf/2020-09/msg00006.html

We should try to bootstrap sage with the new version to make sure everything works before any end-users get a chance to.

This ticket also unbreaks make targets such as distclean, which rely on normal return from ./bootstrap, for these on autoconf 2.71

Upstream: Not yet reported upstream; Will do shortly.

CC: @mkoeppe @kiwifb @dimpase @vbraun

Component: build

Author: Dima Pasechnik, Michael Orlitzky

Branch: 9bfbc41

Reviewer: Dima Pasechnik, Matthias Koeppe

Issue created by migration from https://trac.sagemath.org/ticket/30668