license of std-gnu11, std-gnu23 modules

[Bruno Haible]

Hi Paul,

The files m4/std-gnu11.m4 and m4/std-gnu23.m4 that you added have a license
notice of GPLv3+. This contradicts the module's license notice, which says
"unlimited" in both cases.

We can't easily change the module's license notice to GPLv3+, because
the module 'c99' depends on std-gnu11, and with it a whole slew of other
modules.

As far as I understand, the code in these two files comes from
autoconf/lib/autoconf/c.m4, which carries a license notice with Autoconf
exception.

So, the fix to the contradiction appears to me to be to change the
license notice of m4/std-gnu11.m4 and m4/std-gnu23.m4 to the following
(copied from autoconf/lib/autoconf/c.m4, with an added URL in the last
sentence).

# This file is part of Autoconf.  This program is free
# software; you can redistribute it and/or modify it under the
# terms of the GNU General Public License as published by the
# Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# Under Section 7 of GPL version 3, you are granted additional
# permissions described in the Autoconf Configure Script Exception,
# version 3.0, as published by the Free Software Foundation.
#
# You should have received a copy of the GNU General Public License
# and a copy of the Autoconf Configure Script Exception along with
# this program; see the files COPYINGv3 and COPYING.EXCEPTION
# respectively.  If not, see <https://www.gnu.org/licenses/> and
# 
<https://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=blob_plain;f=COPYING.EXCEPTION>.

Do you agree with that?

Bruno