bug#39865: 28.0.50; Emacs crash

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Fri, 13 Mar 2020 10:35:14 +0100
> Cc: 39865@debbugs.gnu.org
> 
> Eli, the patch as it stands is not suitable for pushing to emacs-27,
> since it breaks the macOS build, which doesnʼt have a
> gui_default_font_parameter function. As far as I can tell (and have
> tested :-) ), we can get away with a dummy one, since there is only
> one font backend on macOS.

I'm okay with doing that.  However, ...

> If you agree, this is what the complete patch looks like:

... this is not how we introduce terminal-dependent methods.  We don't
define different versions of gui_SOMETHING functions in each
terminal-specific back-end.  Instead, we add a member to 'struct
redisplay_interface', and then assign a different value to it in each
back-end.  See how x_redisplay_interface, w32_redisplay_interface,
etc. are defined in the respective *term.[cm] files, and how they are
used via the FRAME_RIF macro.