Cairo font selection for Ethiopic

[Stephen Berman]

I don't know if this is a bug or just the way Cairo works.  On two
different GNU/Linux systems I have built Emacs both --with-cairo and
without.  The non-Cairo builds use Xft as the font backend.  On those
builds the Ethiopic scripts (Amharic and Tigrinya) in HELLO are
displayed with the Goha-Tibeb Zemen font.  In the Cairo builds this font
is not used for these scripts; instead, on one system they are displayed
with a mix of GNU Unifont and mutt-clearlyu, and on the other system,
which lacks these fonts, only hex boxes are displayed.  Is there
something about Goha-Tibeb Zemen that is incompatible with Cairo?

Steve Berman