Disabling universal on Mojave

[Perry E. Metzger]

It's relatively important that
https://github.com/macports/macports-base/pull/107
get dealt with relatively soon. There are significant ports that fail
to build for Mojave because universal builds fail.

If we can't deal with it reasonably quickly, can we rig up the
universal portgroup to disable universal on Mojave until 107 gets
committed?

Perry
-- 
Perry E. Metzger		pmetzger at macports.org