Tier 2 targets

Now that Cargo deduplicates diagnostics from different targets, this doesn't flood the console with
duplicate errors.

Note that this doesn't add `--all-targets` in `Builder::cargo` directly because `impl Step for Std`
actually wants to omit `--all-targets` the first time while it's still building libtest.

When passed `--all-targets`, this warns that the option isn't needed, but still continues to compile.

Also fixed capitalization of documentation

The currently pinned version doesn't compile with the latest rustc nightly

Co-authored-by: Eric Huss <eric@huss.org>
Co-authored-by: inquisitivecrystal <22333129+inquisitivecrystal@users.noreply.github.com>
Co-authored-by: Mark Rousskov <mark.simulacrum@gmail.com>
Co-authored-by: Daniel Giger <danielg3432@gmail.com>

functions marked with #[default_method_body_is_const] would
ICE when being const checked due to it not being a const function:
`tcx.is_const_fn_raw(did)` returns false. We should skip this assert
when it is marked with that attribute.

[rustdoc] Copy only item path to clipboard rather than full `use` statement.

The (somewhat) recent addition of the "copy item import to clipboard" button is extremely nice.

However, i tend to write my code with fully qualified paths wherever feasible and only resort to `use` statements as a refactoring pass. This makes the "copy to clipboard" workflow awkward to use, as i would be copy-pasting that as, say

```rust
impl use std::ops::Add; for MyType {
```

and then go back  and remove the `use ` and `;`.

This PR removes the `use ;` decorations, making it much nicer to use for fully-qualified items. I argue, however, that this does not noticeably degrade experience for those who prefer to import items, since the hard part about those is getting the path right, and writing the `use ;` decoration can be done by hand with little effort.

…bini

Adding explicit notice of lack of documentation for Tier 2 Platforms

Fixing: rust-lang/rustup#2788

…-suggestions, r=estebank

Closure migration multispan suggestions

This changes the `rust_2021_incompatible_closure_captures` lint to only suggest inserting the parts that need to be inserted, instead of suggesting to replace the entire closure by an almost identical closure with one statement added.

Before:
```
[...]
help: add a dummy let to cause `a` to be fully captured
   |
5  ~     let _ = || {
6  +         let _ = &a;
7  +         dbg!(a.0);
8  +         println!("1");
9  +         println!("2");
10 +         println!("3");
 ...
   |

[...]
help: add a dummy let to cause `b` to be fully captured
   |
14 |     let _ = || { let _ = &b; dbg!(b.0); };
   |                ~~~~~~~~~~~~~~~~~~~~~~~~~~

[...]
help: add a dummy let to cause `c` to be fully captured
   |
16 |     let _ = || { let _ = &c; dbg!(c.0) };
   |                ~~~~~~~~~~~~~~~~~~~~~~~~~
```

After:
```
[...]
help: add a dummy let to cause `a` to be fully captured
   |
5  ~     let _ = || {
6  +         let _ = &a;
   |

[...]
help: add a dummy let to cause `b` to be fully captured
   |
14 |     let _ = || { let _ = &b; dbg!(b.0); };
   |                  +++++++++++

[...]
help: add a dummy let to cause `c` to be fully captured
   |
16 |     let _ = || { let _ = &c; dbg!(c.0) };
   |                +++++++++++++           +
```

…pans, r=cjgillot

Detect fake spans in non_fmt_panic lint.

This addresses rust-lang#87621

Some proc_macros claim that the user wrote all of the tokens it outputs, by applying a span from the input to all of the produced tokens. That can result in confusing suggestions, as in rust-lang#87621. This is a simple patch that avoids suggesting anything for `panic!("{}")` if the span of `"{}"` and `panic!(..)` are identical, which is normally not possible.

…mulacrum

Enable `--all-targets` for `x.py check` unconditionally

Now that Cargo deduplicates diagnostics from different targets, this doesn't flood the console with
duplicate errors.

Note that this doesn't add `--all-targets` in `Builder::cargo` directly because `impl Step for Std`
actually wants to omit `--all-targets` the first time while it's still building libtest.

When passed `--all-targets`, this warns that the option isn't needed, but still continues to compile.

Fixes rust-lang#87846.
r? ``@Mark-Simulacrum``

Assign FIXMEs to me and remove obsolete ones

Also fixed capitalization of documentation

We also don't need to transform predicates to be non-const since we basically ignore const predicates in non-const contexts.

r? `````@oli-obk`````

…-Simulacrum

Update redox_syscall

The currently pinned version doesn't compile with the latest rustc nightly

cc ``@jackpot51``

…rk-Simulacrum

Update RELEASES.md for 1.55.0

Reopening rust-lang#87624 after some edits and a force-push caused GitHub to close the PR.

Skip assert ICE with default_method_body_is_const

functions marked with #[default_method_body_is_const] would
ICE when being const checked due to it not being a const function:
`tcx.is_const_fn_raw(did)` returns false. We should skip this assert
when it is marked with that attribute.

r? `@oli-obk`

…aumeGomez

Rustdoc font test

 Add a font test based on rust-lang#85669 fixes rust-lang#85632.

r? `@jsha` `@GuillaumeGomez`