bug#51368: 29.0.50; `cl-case' should error on incorrect use

[Lars Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> BTW, there's a third issue which is that
>
>     (cl-case EXP
>       ((a b) FOO)
>       ((a c) BAR))
>
> won't warn about the duplicate `a`.
>
> After fixing this, many/most uses of `quote` will already emit
> a warning, so maybe it would make the quote/function part of your second
> patch unnecessary.

I think it's nice to have an explicit error case for the quote case so
that the warning can be better, though, so I've pushed Philipps patches
to Emacs 29.

But this test case should also emit a warning.  Philipp, you don't
happen to have a fix for that one, too?  😀