How to handle future compatibility lints

[bjorn3]

Should ferrocene mandate that they are denied, or should it allow them to be silenced? And should there be a difference between future compatibility lints that fix soundness holes and those that don't?

[Veykril]

The current plan is to omit future compat lints, that is we will not specify them, though as the target version of the language that we want to specify is not yet finalized we'll keep an eye on them as some could turn into a hard error by the time we lock in on a version of the language.