This libtool patch isn't applied upstream yet but it is
already used by several projects to fix build failures
on the latest MacOS X (Big Sur).

Upstream patch at https://lists.gnu.org/archive/html/libtool-patches/2020-06/msg00001.html
applies to libtool.m4 but we have to apply it to configure
after autoconf used the (buggy) libtool.m4 instead.

See also open-mpi/ompi#8218.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
(cherry picked from commit d1ef509505d776a8251bcafaa00e888b106100a1)