Deleted unused labels from compiler and fixed or allowed
unused labels in tests. This patch removes some gratuitous
unused labels and turns off the warning for unused labels
that are a necessary part of tests.  This will permit
setting the `unused_labels` lint to `warn`.

Closes rust-lang#66324.

…nneeded Index impl, remove body fn

rustc_codegen_ssa: Fix BodyAndCache reborrow to Body and change instances of body() call to derefence
rustc_mir: Fix BodyAndCache reborrow to Body and change intances of body() call to derefence

`legacy_disrectory_ownership` vs `legacy_directory_ownership`

Change unused_labels from allow to warn

Fixes rust-lang#66324, making the unused_labels lint warn instead of allow by default. I'm told @rust-lang/lang will need to review this, and perhaps will want to do a crater run.

Cleanup BodyCache

After this PR:

- `BodyCache` is renamed to `BodyAndCache`
- `ReadOnlyBodyCache` is renamed to `ReadOnlyBodyAndCache`
- `ReadOnlyBodyAndCache::body` fn is removed and all calls to it are replaced by a deref (possible due to fix of its `Deref` imp in rust-lang#65947)

cc @eddyb @oli-obk

use `#[allow(unused_attributes)]` to paper over incr.comp problem

Paper over the problem in rust-lang#58633.

r? @Mark-Simulacrum

…chenkov

Make `ForeignItem` an alias of `Item`.

Working towards the merging of items in AST and syntactically.

r? @petrochenkov

Fixes typo

`legacy_disrectory_ownership` vs `legacy_directory_ownership`