font chooser widget: Add missing build flags
If we detect HarfBuzz and PangoFT2, GtkFontChooserWidget uses them. So we need to add CFLAGS and LIBS of them to GTK_DEP_CFLAGS/LIBS. If we don't add them, MinGW build fails to link.
If we detect HarfBuzz and PangoFT2, GtkFontChooserWidget uses them. So we need to add CFLAGS and LIBS of them to GTK_DEP_CFLAGS/LIBS. If we don't add them, MinGW build fails to link.