configure.ac:32: warning: The macro `AM_PROG_LIBTOOL' is obsolete.
configure.ac:32: You should run autoupdate.
m4/libtool.m4:100: AM_PROG_LIBTOOL is expanded from...
configure.ac:32: the top level
slg@lastdance src % autoconf -V
autoconf (GNU Autoconf) 2.71
Copyright (C) 2021 Free Software Foundation, Inc.
License GPLv3+/Autoconf: GNU GPL version 3 or later
<https://gnu.org/licenses/gpl.html>, <https://gnu.org/licenses/exceptions.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Written by David J. MacKenzie and Akim Demaille.
slg@lastdance src %
For autoconf 2.71 this creates errors: