bug#28236: 'configure --with-cairo' causes 'emacs -font' to fail

[andrei.elkin@pp.inet.fi]

Hello.

I've been checking out the master branch periodically for quite a while but never
configured it with cairo.
Today I gave it a try, appending the option to my regular option list, as below.

$ git show HEAD
commit 579890f1c7703cd8ecfe2e56f52cc06fcd1b2442
Author: Eli Zaretskii <eliz@gnu.org>
Date:   Fri Aug 25 18:01:19 2017 +0300

  bash# ./configure --with-xft --with-x-toolkit=lucid --with-dbus \
                    --with-cairo && make ...
  => ... [ ok ]
The resulted executable complains about a font that otherwise
"orthodoxically" built one never has done (as the font really exists,
 which xlsfonts double-proves:

  bash# xlsfonts | grep 7x14
  =>7x14
).

  bash# src/emacs -Q -font 7x14
  => Font ‘7x14’ is not defined

This effect is observed in earlier commits as well. (I first suspected the
failure was introduced by a commit in the range started from my last
pull (about two weeks ago)).

I've not investigated any further, still hope this report is not in
vain.

Using this chance, thank you all for working and maintaining this
wonderful piece of software!

Andrelkin.