- Test the combinations of --check-cfg with partial values() and --cfg
- Test that we detect unexpected value when none are expected

…r=cjgillot

Remove in band lifetimes

As discussed in t-lang backlog bonanza, the `in_band_lifetimes` FCP closed in favor for the feature not being stabilized. This PR removes `#![feature(in_band_lifetimes)]` in its entirety.

Let me know if this PR is too hasty, and if we should instead do something intermediate for deprecate the feature first.

r? `@scottmcm` (or feel free to reassign, just saw your last comment on rust-lang#44524)
Closes rust-lang#44524

…rochenkov

Improve `--check-cfg` implementation

This pull-request is a mix of improvements regarding the `--check-cfg` implementation:

- Simpler internal representation (usage of `Option` instead of separate bool)
- Add --check-cfg to the unstable book (based on the RFC)
- Improved diagnostics:
    * List possible values when the value is unexpected
    * Suggest if possible a name or value that is similar
- Add more tests (well known names, mix of combinations, ...)

r? `@petrochenkov`

…ointer, r=michaelwoerister

properly handle fat pointers to uninhabitable types

Calculate the pointee metadata size by using `tcx.struct_tail_erasing_lifetimes` instead of duplicating the logic in `fat_pointer_kind`. Open to alternatively suggestions on how to fix this.

Fixes rust-lang#94149

r? `@michaelwoerister` since you touched this code last, I think!

…i-obk

Normalize main return type during mono item collection & codegen

The issue can be observed with `-Zprint-mono-items=lazy` in:

```rust
#![feature(termination_trait_lib)]
fn main() -> impl std::process::Termination { }
```
```
BEFORE: MONO_ITEM fn std::rt::lang_start::<impl std::process::Termination> `@@` t.93933fa2-cgu.2[External]
AFTER:  MONO_ITEM fn std::rt::lang_start::<()> `@@` t.df56e625-cgu.1[External]
```

update auto trait lint for `PhantomData`

cc rust-lang#93367 (comment)