bug#34256: 27.0.50; Crash on draw_glyphs()

[Eli Zaretskii <eliz@gnu.org>]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Wed, 30 Jan 2019 11:35:32 -0500
> Cc: 34256@debbugs.gnu.org
> 
> Understood. I built that emacs with -O2 and without " --enable-checking='yes,glyphs'
> --enable-check-lisp-object-type" as it's my daily driver version.

I recommend always using these options when building the master
branch.

> I'll work on getting a recipe.

Thanks.

>  Why isn't there a -g3 in the compiler switches?  AFAIK, the default
>  configuration supplies it.
> 
> Yes, I did not add that switch; I do that in my debug builds.

Well, please always use that when you build the master branch.  It's
potentially buggy code, so we need every possible piece of supporting
information to identify and solve bugs reported b y users.

> This was built using the latest master (i.e. with pdumper and no harfbuzz). 

Makes sense.  In that case, it is even more important to find the
reason for this, as there aren't supposed to be display-related
changes on master, so stuff like x_draw_glyph_string isn't supposed to
get in trouble.

Thanks.