Reminder to self:

echo "https://ftp.eu.openbsd.org/pub/OpenBSD/" >/etc/installurl
pkg_add git autoconf automake libtool

Select the latest versions, then add the following to ~/.profile:

AUTOCONF_VERSION=2.69
AUTOMAKE_VERSION=1.15
export AUTOCONF_VERSION AUTOMAKE_VERSION

With your selected versions, of course.