https://bugs.openldap.org/show_bug.cgi?id=9485
--- Comment #8 from kloczko.tomasz@gmail.com kloczko.tomasz@gmail.com ---
OpenLDAP 2.4 requires autoconf 2.59, and that will not change as it's not open for development.
Issue is that correctly done changes for ac 2.71 will be 100% backlward compatible with ac 39.