bug#25706: 26.0.50; Slow C file fontification

[Alan Mackenzie]

Hello again, Mattias.

On Mon, Nov 30, 2020 at 18:04:56 +0100, Mattias Engdegård wrote:
> > Actually, it's the underscores!

> Found it. Suggested fix attached.

> It can be improved: at least one pair of regexp group brackets can be
> removed, but I didn't dare doing so because I wasn't sure if it would
> throw some group numbers off by one.

> Alan, please, let's work together and remove unnecessary capture groups
> from the regexps! Even XEmacs regexps support non-capturing brackets,
> \(?:...\), and they save time, regexp stack space, and reduce the
> hassle of computing the 'regexp depth' everywhere.

There are 342 occurrences of '\\\\([^?]' in CC Mode.  Most of these can
surely be replaced by "\\(?:", but not all, by a long way.  This change
will be fun.

-- 
Alan Mackenzie (Nuremberg, Germany).