add an off-by-default lint for catching constant statics

[thestinger]

Crates not concerned about providing a stable ABI for global variables should be able to opt-in to a lint to deny constant statics. This would catch regressions due to the removal of inlining and insignificant addresses for constant static variables (#18311).

[thestinger]

It would always make sense to lint for private statics.

[steveklabnik]

Traige: no change.

[steveklabnik]

Since new lints have a big impact on users of rustc, the policy is that they should go through the RFC process like other user-facing changes. As such, I'm going to give this one a close, but if anyone comes across this ticket and wants this lint, consider adding it to clippy and/or writing up an RFC. Thanks!