Regenerate with approved autotools version

[Nick Alcock]

On 14 Jun 2019, Alan Modra uttered the following:

> Someone apparently used a distro autotools.

Well, I certainly didn't. What I did was use a system autoconf v2.69
checked out and built via the tag from the git repo, rather than going
through the whole make dist / untar / build / install dance. It turns
out this produces an Autoconf different from one generated via make
dist, in that the version number it embeds in generated configure
scripts is blank (though if I try doing the make dist-and-build dance, I
end up with a tree described as -dirty even though it isn't, and the
Autoconf generated is even more different: if I use git archive first,
the thing ends up bizarrely described as being autoconf-UNKNOWN. I gave
up after that.)

I can only assume that the autoconf-2.69.tar.xz on the GNU site has been
generated via some deep magic I do not have access to, since neither
straight building, nor "make dist" from a git repo, nor "git archive"
followed by make dist from the expansion produce the same content as the
tarball.

So I'll use an autoconf installed from the upstream tarball from now on.