bug#45550: [PATCH] Factor out new function for readability in chartab.c

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Wed, 30 Dec 2020 15:16:05 -0600
> Cc: 45550@debbugs.gnu.org
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Please make this a macro, not a function.  The code you are factoring
> > out is called in the innermost loops of the display engine, in bidi.c,
> > so it must be as fast as possible, even in an unoptimized build, where
> > static functions aren't inlined.
> 
> Would it be acceptable to use our INLINE macro here instead?

I'd prefer a simple macro.  I can never remember the exact semantics
of INLINE this week.

Thanks.