bug#56682: Fix the long lines font locking related slowdowns

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

> And I've found a serious sink of CPU cycles under truncate-lines, and
> installed a fix on the feature branch.  Gerd, if you have time to
> eyeball the fix and comment on it, I'd appreciate.  It's commit
> 350e97d on the branch.  (I can post a more detailed explanation of
> what I did and why, if that would help, because the code and the
> functions it calls are somewhat tricky.)

I'll look at it and come back.

BTW, does feature/long-lines-and-font-locking] build for you?  I'm getting

In toplevel form:
cedet/semantic/symref/list.el:35:2: Error: Wrong type argument: 
number-or-marker-p, nil
make[2]: *** [cedet/semantic/symref/list.elc] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [compile-main] Error 2
make: *** [lisp] Error 2

Configured --with-native-compilation.