bug#11786: Use c_strcasecmp for portable ASCII case-insensitive comparison

[Eli Zaretskii]

> Date: Tue, 26 Jun 2012 10:25:17 -0700
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: Andreas Schwab <schwab@linux-m68k.org>, dmantipov@yandex.ru, 
>  11786@debbugs.gnu.org
> 
> c_strcasecmp does what you're saying (it uses c_tolower), and it's
> off-the-shelf code

So is xstrcasecmp.

> This shrinks and simplifies the source code of Emacs proper.

Your change neither shrinks nor simplifies anything.  It does the
exact opposite, in fact.