[Bug c/63499] gcc treats unknown -Wno-xxx options differently than -Wxxx

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63499

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Zbigniew Jędrzejewski-Szmek from comment #3)
> So, there's no way to programmatically check whether a flag is supported,
> without resorting to grepping the output or something like that. Great.

No there is way just use the positive side rather than the no- option.