More recent versions of harfbuzz conveniently generate harfbuzz.cc
which has the full list of source files, so point our build to
that instead of chasing the evolving list of files: much easier!
Fixup some of the predefined symbols, and include opentype functions
in bindings.h so that we can pick those up in the bindgen output.
This is primarily for macos where the default freetype
installation is unable to render color emoji, but should also
help make things more consistent across the various platforms.
It's a little bit awkward on linux because the font-loader crate
pulls in the now-conflicting servo-font* crates. I've disabled
font-loader on linux systems; it's just calling fontconfig under
the covers anyway.
