Opt-in pkg-fallout@ mail to maintainers from Tier2 architectures

[Jan Beich]

Fixing Tier2 bustage is often non-trivial due to complicated triaging and
testing. Maintainers are better positioned to come up with fixes. Sometimes
Tier* archs change over the years or committers mark ports BROKEN en masse
without giving maintainers a chance to fix in advance. However, pkg-fallout@
is a noisy list thus requires heavy filtering that in itself has to be
maintained to not grow out of sync.

Is there a easy way to subscrube to bustage e.g., on aarch64?

Related:
https://lists.freebsd.org/pipermail/freebsd-ports/2015-June/099438.html
https://lists.freebsd.org/pipermail/freebsd-ports/2013-August/085568.html