Revert "ffmpeg 4.2: Remove --enable-libass."
Revert "ffmpeg 4.2: Remove --enable-libass."

This reverts commit 9aa29de3929bc3c11a4db958a5f4441b9100bb45.

I actually can't reproduce the failure seen on buildmaster. That's
not a good sign.

Begasus/haikuports,Begasus/haikuports,haikuports/haikuports,haikuports/haikuports,haikuports/haikuports,Begasus/haikuports,Begasus/haikuports,Begasus/haikuports,haikuports/haikuports,haikuports/haikuports