bug#22884: 25.0.92; C/l mode editing takes waaaayy too long

[Eli Zaretskii]

> Date: Thu, 3 Mar 2016 12:49:10 +0000
> From: Alan Mackenzie <acm@muc.de>
> Cc: 22884@debbugs.gnu.org
> 
> > emacs -Q config.h
> > M-x goto-line RET 1661 RET / /
> 
> > On my six-year-old desktop the second '/' takes about 10 seconds to 
> > echo.  This sort of thing makes Emacs effectively unusable for editing 
> > config.h.
> 
> The problem is in config.h.  At line 14, inside a comment, appears the
> following string:
>     "(at your option) any later version."
> .  The open paren is at column zero, so the fancy code in syntax.c then
> fails to recognise the comment as a comment.

I think we should change syntax.c to fix this.  (Alternatively, CC
mode could stop depending on it, but I doubt this is a viable
alternative.)  We cannot really tell people we don't support such
files, as they are valid C code.