[HarfBuzz] Building and testing HarfBuzz 2.3.0 on MinGW

[Eli Zaretskii]

> From: Ebrahim Byagowi <ebraminio at gmail.com>
> Date: Sun, 27 Jan 2019 01:02:01 +0330
> Cc: Harfbuzz <harfbuzz at lists.freedesktop.org>
> 
> 1) Agreed

Btw, one other prerequisite for running the test suite is Python.  I
suggest that to be mentioned as well.  In my case, Python was not on
PATH, and most tests failed.

> 2) Something feels wrong as we compile all these in our msys2 CI already and that shouldn't be that different
> from your setup

I saw that similar failures were reported here:

  https://github.com/harfbuzz/harfbuzz/issues/1560

So I upgraded my Freetype 2.5.0.1 to the latest 2.9.1, and then all
the tests passed.  Therefore, I suggest that the oldest version of
Freetype that is considered "good enough" for the test suite be
referenced in the documentation of prerequisites for running the
tests.

> 3) Uniscribe and DirectWrite backends and now CoreText, are mostly for comparison while development, so
> developers can check what can be expected behavior while development, and are not used in the test suit at
> least which tends to be platform agnostic so don't use them at all if you can.

Got it, thanks.