The API this exposes is a little strange (being attached to `static`s),
so it makes sense to conservatively feature gate it. If it is highly
popular, it is possible to reverse this gating.
static_assert is documented as working on static with type `bool`, but
we currently accept it on any const static and crash when the const has
an non-integral type.
This is a breaking-change for anyone who used static_assert on types
likes i32, which happened to work but seems like an unintended
consequence of the missing error checking.
[breaking-change]
Fixes#22056