GPL-3+-with-autoconf-exception

GNU General Public License, version 3 or any later version.
See GPL-3 for the full text of this license.

As a special exception to the GNU General Public License, if you
distribute this file as part of a program that contains a
configuration script generated by Autoconf, you may include it under
the same distribution terms that you use for the rest of that
program.  This Exception is an additional permission under section 7
of the GNU General Public License, version 3 ("GPLv3").