On Windows HarfBuzz and PangoFT2 are optional, so we need to ensure that
we only build the bits that require HarfBuzz and PangoFT2 when needed.
We may need to see later whether we can get the needed functionality in
gtkfontchooserwidget.c with the Windows APIs without the need of
HarfBuzz nor PangoFT2 (and starting programs on Windows using FontConfig
is very slow).
Remove g_auto*() usage from these sources and use the traditional
g_free(), as g_auto*() are GCCisms (or CLangisms).
Also, don't include unistd.h unconditionally and stop including
langinfo.h and dirent.h, since they seem to be unused.
Partially cherry-picked from a4c0395343c3969c330cb37efa45ae952ba74b86
https://bugzilla.gnome.org/show_bug.cgi?id=773299