Sigh, spent one day, more or less, tracking down a weird fontconfig
problem, where all the diagnostic it offered was "unknown encoding"
when reading the fonts.conf file.

It turned out that I was being screwed by our fun two versions of the
expat_xmlparse library: One where XML_Char is char and one where it is
short. The intuitively "more normally" named libexpat_xmlparse is the
latter, but fontconfig works only with the former as it implicitly
expects XML_Char to be char.