Auto merge of #36866 - alexcrichton:fix-hash-again, r=eddyb

rustc: More fixes for arch-independent hashing

In another attempt to fix #36793 this commit attempts to head off any future
problems by adding a custom `WidentUsizeHasher` which will widen any hashing of
`isize` and `usize` to a `u64` as necessary. This obviates the need for a
previous number of `as u64` annotations and will hopefully protect us against
future problems here.

Closes #36793 (hopefully)