Due to how ninja runs clang and gcc, it doesn't colorize the output
like make does. This forces color output in this situation.

This adds support for introspection builds on Windows that is enabled by
the HB_HAVE_INTROSPECTION option, which will also enable HB_HAVE_GOBJECT
(and so HB_HAVE_GLIB) as they are required for introspection.

In order for this to work one must ensure that the Python installation
listed in PYTHON_EXECUTABLE is the same Python release series that was
used to build _giscanner.pyd (the Python module that is used by
g-ir-scanner), with the same architecture.  PKG_CONFIG_PATH and PATH
must be set correctly if $(PREFIX)\bin and/or $(PREFIX)\lib\pkgconfig
are not in the standard PATH and PKG_CONFIG_PATH, which is actually
in-line with the *NIX builds.

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.

Include the fallback sources in the build, and update
src/Makefile.sources so that it can be read by the CMake build files.

Fix a typo in the DirectWrite configure option so that we can properly
enable DirectWrite builds.

Also, when building the utility program, install them as well.

Instead of searching for freetype using pkg-config, use the FindFreetype
feature of CMake. This allows for better integration with other projects
that make use of CMake.

Fixes https://github.com/behdad/harfbuzz/issues/518