Fix warnings in `Vc` that arise when compiling ROOT

[guitargeek]

When including Vc.h, ROOT Math disables several compiler diagnostics to avoid warnings in the CI and nightlies:
https://github.com/root-project/root/blob/0fd27057b7b25e777ea642dfcc216ab27a6ece0d/math/mathcore/inc/Math/Types.h

It would be good if any warnings can be avoided in upstream veccore, such that we don't need this hack in ROOT.

See also root-project/veccore#24.

[bernhardmgruber]

Hi! Vc is no longer developed. If you can provide a PR, I can help you get it in. In the long term I would try to migrate to std::simd. There is a fallback implementation available if you have to support compilers without std::simd: https://github.com/mattkretz/vir-simd

[dpiparo]

for the time being: #356 . If you are happy with the pr, your test suite and nightlies pass, could you tag a new version so that it can be included e.g. in ROOT? Thanks a lot in advance!!

[bernhardmgruber]

I merged the PR on Vc.

[bernhardmgruber]

@guitargeek, does PR #356 entirely solve this issue?

[guitargeek]

No, not entirely. It solves the current remaining warning in the nighlies, yes, but we have still "hotfixed" away several warnings in ROOT Math:
https://github.com/guitargeek/root/blob/master/math/mathcore/inc/Math/Types.h#L11

Once Vc is in a state where we get no warnings in the ROOT nightlies without the pragmas, then I would consider this issue as solved.

Thanks for the work you have done already, @bernhardmgruber and @dpiparo 👍