Version 0.2.150 include support for the new check-cfg syntax

Two places called `from_utf8_unchecked` for strings from `alloc_slice`,
and one's SAFETY comment said this was for lack of `alloc_str` -- so
let's just add that instead!

Change the implementation of `Instance::is_foreign_item` to directly
query the compiler for the instance `def_id` instead of incorrectly
relying on the conversion to `CrateItem`.

Background:

- In pull rust-lang#118524, I fixed the
  conversion from Instance to CrateItem to avoid the conversion if the
  instance didn't have a body available. This broke the `is_foreign_item`.

This is much cheaper than building a body just for the purpose of
checking if the body exists.

…syntax, r=b-naber

Remove deprecated `--check-cfg` syntax

This PR removes the deprecated `--check-cfg` `names(...)` and `values(...)` syntax.

Follow up to rust-lang#111072
Part of rust-lang/compiler-team#636

r? compiler

… r=cuviper

Suppress warnings in LLVM wrapper when targeting MSVC

The LLVM header files generate many warnings when compiled using MSVC. This makes it difficult to work on the LLVM wrapper code, because the warnings and errors that are relevant to local edits are obscured by the hundreds of lines of warnings from the LLVM Headers.

tip for define macro name after `macro_rules!`

Fixes rust-lang#118295

~Note that there are some bad case such as `macro_rules![]` or `macro_rules!()`. However, I think these are acceptable as they are likely to be seldom used (feel free to close this if you think its shortcomings outweigh its benefits)~

Edit: this problem was resolved by utilizing the `source_map.span_to_next_source`.

r? `@petrochenkov`

…Lapkin

Enforce `must_use` on associated types and RPITITs that have a must-use trait in bounds

Warn when an RPITIT or (un-normalized) associated type with a `#[must_use]` trait in its bounds is unused.

This is pending T-lang approval, since it changes the semantics of the `#[must_use]` attribute slightly, but I think it strictly catches more strange errors.

I could also limit this to just RPITITs, but that seems less useful.

Fixes rust-lang#118444

rustc_arena: add `alloc_str`

Two places called `from_utf8_unchecked` for strings from `alloc_slice`,
and one's SAFETY comment said this was for lack of `alloc_str` -- so
let's just add that instead!

Fix is_foreign_item for StableMIR instance

Change the implementation of `Instance::is_foreign_item` to directly query the compiler for the instance `def_id` instead of incorrectly relying on the conversion to `CrateItem`. I also added a method to check if the instance has body, since the function already existed and it just wasn't exposed via public APIs. This makes it much cheaper for the user to check if the instance has body.

## Background:

- In pull rust-lang#118524, I fixed the conversion from Instance to CrateItem to avoid the conversion if the instance didn't have a body available. This broke the `is_foreign_item`.

r? `@ouz-a`