idna uses unicode_compat_util, and downloads it from the net and
builds it. This wasn't installed, and thus any attempt to use idna
failed at runtime, breaking s2s in ejabberd with earlier erlang-xmpp,
and probably breaking everything with current erlang-xmpp.
The idna library has removed this library, but doesn't have a release
yet. So this problem should go away soonish. For now, accept the ick
to (very likely) unbreak ejabberd.
(This commit does not increase the use of the net during the build; it
merely uses the build products that already happened.)
ad0959afe5