Return canonicalized paths from FcConfigRealFilename

FcConfigRealFilename() follows symlinks, but the link may be relative to the
directory containing the link.  For example, on my system, I have this file:

/etc/fonts/conf.d/99-language-selector-zh.conf ->
    ../conf.avail/99-language-selector-zh.conf

Since /etc/fonts/conf.d is probably not in PATH, open()ing the file would fail.
This change makes FcConfigRealFilename() return the canonicalized filename
instead.  So for the example above, it would return:

/etc/fonts/conf.avail/99-language-selector-zh.conf

This was causing bad font rendering in Chromium [1] after the regression I
introduced in 7ad010e80bdf8e41303e322882ece908f5e04c74.

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=857511
3 files changed