bug#29713: 26.0; Provide completion for `make-frame-on-display'

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Date: Wed, 24 Mar 2021 21:59:42 +0000
> Cc: 29713@debbugs.gnu.org, Lars Ingebrigtsen <larsi@gnus.org>
> 
> > Or maybe better to fall back to 'make-frame'?
> > I.e. don't signal an error, don't ask a question,
> > just create a new frame on the current display.
> >
> > So on --without-x builds, make-frame-on-display
> > could be like an alias to make-frame.
> 
> I have no strong preference between this option or just signalling an
> error in the interactive spec.  What do others think?

I think we should signal an error: the user will not get what they
want, so the user must be told.