Hash `Kind` in metadata for crates

Hash `Kind` in metadata for crates

This fixes what is now a bug in Cargo discovered when attempting to land
rust-lang/rust#42495 where Cargo will compile both host and target artifacts
with the same `-C metadata` flag. This means that the compile can load two
crates with the same SVH that are supposed to be distinct, which causes weird
bugs with crate loading and whatnot.

This commit throws in the `Kind` into the metadata calculation to resolve this
to ensure that host/target artifacts always have a different `-C metadata`