bug#33771: 27.0.50; Error building Harfbuzz branch on Debian testing

[Eli Zaretskii]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Mon, 17 Dec 2018 18:20:28 +0100
> Cc: Mike Kupfer <mkupfer@alum.berkeley.edu>, 33771-done@debbugs.gnu.org, 
>       far.nasiri.m@gmail.com
> 
> Thanks, it seems to build now without errors.
> I still get a few warnings though:
> 
>   CC       ftfont.o
> ftfont.c:2819:1: warning: ‘ftfont_shape_by_hb’ defined but not used
> [-Wunused-function]
>  ftfont_shape_by_hb (Lisp_Object lgstring, FT_Face ft_face, hb_font_t 
> *hb_font,
>  ^~~~~~~~~~~~~~~~~~
> ftfont.c:482:1: warning: ‘ftfont_get_hb_font’ defined but not used
> [-Wunused-function]
>  ftfont_get_hb_font (struct ftfont_info *ftfont_info)
>  ^~~~~~~~~~~~~~~~~~

I tried to fix that, please test.