[Bug testsuite/80092] Add effective-target keywords for unsupported nvptx features

[vries at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80092

--- Comment #15 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Martin Liška from comment #14)
> Tom: Can you please update Known to work?

This work isn't done, so I think it's valid as it is: empty.

Thanks,
- Tom