bug#43177: Bug: Emacs 27.1 hangs forever in `FcCharSetSubtractCount' from '/usr/lib/libfontconfig.so.1'

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Date: Thu, 03 Sep 2020 17:10:30 +0200
> Cc: 43177@debbugs.gnu.org, Alexander Shukaev <emacs@Alexander.Shukaev.name>
> 
> >>>>> On Thu, 03 Sep 2020 16:48:04 +0200, Andreas Schwab 
> >>>>> <schwab@linux-m68k.org> said:
> 
>     Andreas> On Sep 03 2020, Robert Pluim wrote:
>     >> Does it go away if you set font-backend . ftcrhb in your frame
>     >> parameters (assuming youʼre using Cairo)?
> 
>     Andreas> That completely removes the delay.
> 
> So the solution is easy: just deprecate and remove the 'x' backend :-)

Easy: yes.  Possible: no.  Unfortunately.

Do we understand why including the x backend produces such a huge
delay?  Where is most of that time spent, and why?