This patch is already in Gnulib since 2020-12-09. But when people
run 'autoreconf' on an existing released tarball, they are effectively
combining an older Gnulib with a newest Autoconf.

Why do people do that? The point of tarballs is that you can run
'./configure' right away.

If people want to modify the build infrastructure, it would often be
more reasonable to start off the git repository of the package (possibly
from a specific release tag or release branch).