> Thanks, you can just remove Haiku from the list.  Otherwise, I'm happy
> now.

Ok, here is the final patch, and a suggested commit message. I've
initiated the paperwork for the copyright assignment, I will let you
know when it is done.

Commit message:

Better check for when clipboard or primary selection have changed

Previously it was done by just comparing new and old selection text, now
we use also selection timestamps for systems that support it (only
enabled in X for now). This fixes bug#53894.

lisp/select.el: new variables gui--last-selection-timestamp-clipboard
and gui--last-selection-timestamp-primary. New functions
gui--set-last-clipboard-selection, gui--set-last-primary-selection,
gui--clipboard-selection-unchanged-p and
gui--primary-selection-unchanged-p.