It has been created by Alexander Kahl from a branch of evol in order to reach a broader audience. One might ask, "why in hell do we need another implementation of this terrifying language?" - it is because generating an AST from M4 code is impossible and GNU M4 doesn't offer enough means of hooking up into macro evaluation, thus only a powerful CL version might enable one to convert M4 or re-utilize libraries like GNU Autoconf.
Warning: Alpha stage!
The package is asdf-installable. The link to the git repository is available from Github.
ASDF-install package (obsolete) http://github.com/e-user/cl-m4/tarball/master