FreeBSD 13.1 had introduced a sched cpu affinity compatibility layer
with Linux. 13.0 and even 13.1 being EOL, we can simplify here.

That is, change `diagnostic_outside_of_impl` and
`untranslatable_diagnostic` from `allow` to `deny`, because more than
half of the compiler has be converted to use translated diagnostics.

This commit removes more `deny` attributes than it adds `allow`
attributes, which proves that this change is warranted.

This rewrite makes the cache-updating nature of the function slightly clearer, using the Entry API into the hash table for region names to capture the update-insert nature of the method. May be marginally more efficient since it only runtime-borrows the map once, but in this context the performance impact is almost certainly completely negligible.

The current order is almost perfectly random. This commit puts them into
a predictable order in their own impl block, going from the highest
level (`Block`) to the lowest (`Expect`). Within each level this is the
order:

- struct_err, err
- struct_span_err, span_err
- create_err, emit_err

The first one in each pair creates a diagnostic, the second one creates
*and* emits a diagnostic. Not every method is present for every level.

The diff is messy, but other than moving methods around, the only thing
it does is create the new `impl DiagCtxt` block with its own comment.

- Remove low-value comments about functionality that is obvious.

- Add missing `track_caller` attributes -- every method should have one.

- Adjust `rustc_lint_diagnostic` attributes. Every method involving a
  `impl Into<DiagnosticMessage>` or `impl Into<SubdiangnosticMessage>`
  argument should have one, except for those producing bugs, which
  aren't user-facing.

…ariants

Introduce `run-make` V2 infrastructure, a `run_make_support` library and port over 2 tests as example

See [issue rust-lang#40713: Switch run-make tests from Makefiles to rust](rust-lang#40713) for more context.

### Basic Description of `run-make` V2

`run-make` V2 aims to eliminate the dependency on `make` and `Makefile`s for building `run-make`-style tests. Makefiles are replaced by *recipes* (`rmake.rs`). The current implementation runs `run-make` V2 tests in 3 steps:

1. We build the support library `run_make_support` which the `rmake.rs` recipes depend on as a tool dylib.
2. We build the recipe `rmake.rs` and link in the support library.
3. We run the recipe to build and run the tests.

`rmake.rs` is basically a replacement for `Makefile`, and allows running arbitrary Rust code.

### Planned Changes

- [x] Get rid of the builder style patterns in `rmake_support` and instead use something like

    ```rust
    let output = rustc!(scx, "--cfg x -Cprefer-dynamic -Csymbol-mangling-version=legacy -
    Zunstable-options");
    ```
    as per Nils' suggestion. This can probably use something like `xshell`.
- [x] Make `run_make_support` into a proper crate so it can have external dependencies like `xshell`.
- [x] Instead of having an entire alternative directory `run-make-v2`, change how V2 tests are collected based on presence of `rmake.rs` recipe file. This should ease migration and prevent git history from being messed up by big moves.

### Disclaimer

The current implementation is very much a **very very rough prototype** just to get the 2 example tests working. I would appreciate any feedback on the design and implementation.

std::thread::available_parallelism merging linux/android/freebsd version

FreeBSD 13.1 had introduced a sched cpu affinity compatibility layer with Linux. 13.0 and even 13.1 being EOL, we can simplify here.

Remove unused args from functions

`#[instrument]` suppresses the unused arguments from a function, *and* suppresses unused methods too! This PR removes things which are only used via `#[instrument]` calls, and fixes some other errors (privacy?) that I will comment inline.

It's possible that some of these arguments were being passed in for the purposes of being instrumented, but I am unconvinced by most of them.

…al-link, r=notriddle

[rustdoc] Correctly generate path for non-local items in source code pages

While browsing some crates using the "jump to def" feature, I realized that a lot of items didn't have a link generated. The reason is because we only cache foreign items if they appear in the documented API. This means that for the others, we need to infer them.

r? ````@notriddle````

…s, r=davidtwco

Invert diagnostic lints.

That is, change `diagnostic_outside_of_impl` and `untranslatable_diagnostic` from `allow` to `deny`, because more than half of the compiler has been converted to use translated diagnostics.

This commit removes more `deny` attributes than it adds `allow` attributes, which proves that this change is warranted.

r? ````@davidtwco````

…write, r=compiler-errors

A drive-by rewrite of `give_region_a_name()`

This drive-by rewrite makes the cache-updating nature of the method clearer, using the Entry API into the hash table for region names to capture the update-insert nature of the method. May be marginally more efficient since it only runtime-borrows and indexes the map once, but in this context the performance impact is almost certainly completely negligible.

Note that this commit should preserve all externally visible behaviour. Notably, it preserves the debug logging:

1. printing even in the case of a `None` for the new computed name, and
2. only printing on new values, begin silent on reused values

…gillot

No need to take `ImplTraitContext` by ref

We used to mutate `ImplTraitContext`, so it used to be `&mut` mutable ref. Then I think it used to have non-`Copy` data in it, so we took it by `&` ref. Now, none of that remains, so just copy it around.

…mpiler-errors

Reorder diagnostics API

The totally random ordering of diagnostic methods in `DiagCtxt` has been low-key driving me crazy for a while now.

r? ````@compiler-errors````

Remove myself from review rotation.

I've been unable to keep up with reviews. :(

Not sure if this helps much, considering there aren't many other libs reviewers on the rotation at the moment.

Hopefully I can add myself back again Soon™ when I can commit more time to reviewing.

…, r=Mark-Simulacrum

Add release note for new ambiguous_wide_pointer_comparisons lint

I found out about this new lint in Rust because I had code allowing the Clippy lint. Clippy alerted me to the lint name change, and I went searching for the new lint's name in the release notes and was surprised there wasn't an item for it.