Autoconf is an extensible package of m4 macros that produce shell
scripts to automatically configure software source code packages.
These scripts alledgedly can adapt the packages to many kinds of UNIX-like
systems without manual user intervention.  Autoconf creates a
configuration script for a package from a template file that lists the
operating system features that the package can use, in the form of m4
macro calls.

The FSF would make you believe that only gnu-m4 can handle autoconf.
As of OpenBSD 2.7, this is no longer true. This package does not depend
on gnu-m4.

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