Unconditional constexpr due to trivial union

[wusatosi]

We need to update current implementation to use union as its storage type.

This is because trivial union (P3074) has been voted into C++26 and made unconditional constexpr possible.

[JeffGarland]

There should be a feature test macro we could check if we wanted to keep the current code and change it if the compiler supports trivial unions. Although maybe that's too complicated?

edit: I see there's another issue to implement -- maybe this is a duplicate?

[wusatosi]

edit: I see there's another issue to implement -- maybe this is a duplicate?

You're right, I will fold this to the other issue.

There should be a feature test macro we could check if we wanted to keep the current code and change it if the compiler supports trivial unions. Although maybe that's too complicated?

It doesn't make sense for us to implement this yet. I don't believe there's any confirmed compiler support yet. Without those we will not be able to test against our implementation.