This adds support to the CMake build files to support building
HarfBuzz-GObject, which is actually a little bit complicated,
as we need to:
-Run glib-mkenums, which is a Python (for newer GLib/GObject) or PERL
(for older, pre 2.53.4, GLib/GObject) script. This matters more for
Visual Studio builds as shebang lines are not supported, so we need to
test-run it with PERL or Python to determine which is the correct
interpretor to use.
-Next, we need to replace strings in the sources that we obtain from
running glib-mkenums. So, the solution here is to use a small utility
CMake script for our purposes here, to maintain maximum compatibility.
-Ensure that things do work in the Visual Studio IDE builds.
Chun-wei Fan