Also, call c++filt on their results.

Also build and fix and check harfbuzz-gobject.def

Also changes harfbuzz-gobject to distribute generated enum sources.

Hopefully most bots come back with this...

Part of https://github.com/behdad/harfbuzz/issues/277

This prepares the headers for exporting symbols using visibility
attributes or __declspec(dllexport), so that we do not need to maintain
symbols listing files, as this is what was and is done in GLib and GTK+.

Based on data from http://upstream-tracker.org/versions/harfbuzz.html
Resolves #103

Using latest gobject-introspection, I don't seem to be having this
problem anymore:

  https://bugzilla.gnome.org/show_bug.cgi?id=707656

Removing that kludge makes language_t behave more like the way I expect it
in Python.

Also fixes:
https://github.com/behdad/harfbuzz/issues/91

Move it to new harfbuzz-gobject library.  Implement enums and
boxed types for object-types.  Still have to do boxed types for
value types.