bug#69706: 30.0.50; sort.c, unnecessary GC marking

[Eli Zaretskii]

> From: Gerd Möllmann <gerd.moellmann@gmail.com>
> Date: Sun, 10 Mar 2024 09:45:01 +0100
> 
> sort.c uses record_unwind_protect_mark to let GC mark some objects in
> its merge_state structure, while GC marks the specpdl stack.
> 
> This is
> 
> - unnecessary because all the objects that are currrently extra
>   protected by merge_markmem, are already seen by the GC, because these
>   are the objects being sorted, which are protected in the usual way
>   (marking the control stack, ...)
> 
> - costs GC time
> 
> - complicates the code
> 
> I therefore suggest removing this, including the removal of
> record_unwind_protect_mark and the mark function pointer in union
> specbinding (sort.c is the only user).

Can you show the patch, please?

Adding Stefan and Mattias to the discussion, in case they have
comments or suggestions.

Thanks.