Auto merge of #115524 - RalfJung:misalign, r=wesleywiser

const-eval: make misalignment a hard error

It's been a future-incompat error (showing up in cargo's reports) since rust-lang/rust#104616, Rust 1.68, released in March.  That should be long enough.

The question for the lang team is simply -- should we move ahead with this, making const-eval alignment failures a hard error? (It turns out some of them accidentally already were hard errors since #104616. But not all so this is still a breaking change. Crater found no regression.)

Author: bors