bug#40180: 27.0.90; cl-concatenate returns wrong result

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Sun, 22 Mar 2020 07:53:31 -0400
> Cc: Joost Kremers <joostkremers@fastmail.fm>, 40180@debbugs.gnu.org
> 
> Stephen Berman <stephen.berman@gmx.net> writes:
> 
> > Similarly, (cl-concatenate 'vector '[a b c] '[d e f]) returns `[[a b c]
> > [d e f]]' and worse, (cl-concatenate 'string "abc" "def") raises the
> > error: Wrong type argument: characterp, "abc".  This is because
> > cl-concatenate is now defined in terms of seq-concatenate, which is
> > defined by cl-defgeneric, which adds an extra pair of parens around the
> > SEQUENCES argument
> 
> I think the problem is just that cl-concatenate should call
> seq-concatenate with apply.

Thanks, please push this to the emacs-27 branch.