bug#53894: 27.2; Clipboard copy -> C-y -> M-y -> Same clipboard copy does not push to kill ring

[Po Lu]

Lars Ingebrigtsen <larsi@gnus.org> writes:

>> It is, `gui-backend-selection-owner-p' does not work reliably on some
>> other platforms such as PGTK and NS.

> Do we have a list of these platforms?  Perhaps we should have a function
> that says whether the `gui-backend-selection-owner-p' results are
> reliable...?

IME, it's PGTK on Wayland and GNUstep where it doesn't work reliably.
It seems to work fine on macOS, and it's guaranteed to work on X (if it
doesn't, then selections won't work at all) and Haiku.

Thanks.