Penn will compile and run on OpenBSD, with the caveats below. Tested
with OpenBSD 6.2.

Using clang instead of gcc is recommended (CC=clang ./configure ...),
as OpenBSD's gcc is a very old version.

Some packages need to be installed via pkg_add or from source if not
already present on the server:

  Required: pcre
  Optional: libevent, mariadb-client, postgresql-client, curl, icu4c.

* OpenBSD will not forward IPv4 connections to a listening IPv6
  port. Specify a generic IPv4 address (0.0.0.0) or specific one in
  mush.cnf instead.

