This allows decoupling `Command::spawn` and `Command::output`. This is
useful for targets which do support launching programs in blocking mode
but do not support multitasking (Eg: UEFI).

This was originally conceived when working on rust-lang#100316

Signed-off-by: Ayush Singh <[email protected]>

* This stops applying a margin to the additional example links.
  Because these links are `display: inline`, it doesn't actually do anything.
* This switches from using a margin-bottom with a special exception for
  the examples themselves, plus an additional margin on the hide button,
  to instead using just margin-top on the examples, with an exception for
  the first one.

No user-visible changes should result from this.

The lint "clippy::uninlined_format_args" recommends inline
variables in format strings. Fix two places in the docs that do
not do this. I noticed this because I copy/pasted one example in
to my project, then noticed this lint error. This fixes:

error: variables can be used directly in the `format!` string
  --> src/main.rs:30:22
   |
30 |         let string = format!("{:.*}", decimals, magnitude);
   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: variables can be used directly in the `format!` string
  --> src/main.rs:39:2
   |
39 |  write!(&mut io::stdout(), "{}", args).unwrap();

…ate per target)

This allows us to use a consistent path in the documentation, without having to worry about which platform people are using.

…ulacrum

Symlink `build/host` -> `build/$HOST_TRIPLE`

(as appropriate per target)

This allows us to use a consistent path in the documentation, without having to worry about which platform people are using.

…imulacrum

Allow blocking `Command::output`

### Problem
Currently, `Command::output` is internally implemented using `Command::spawn`. This is problematic because some targets (like UEFI) do not actually support multitasking and thus block while the program is executing. This coupling does not make much sense as `Command::output` is supposed to block until the execution is complete anyway and thus does not need to rely on a non-blocking `Child` or any other intermediate.

### Solution
This PR moves the implementation of `Command::output` to `std::sys`. This means targets can choose to implement only `Command::output` without having to implement `Command::spawn`.

### Additional Information

This was originally conceived when working on rust-lang#100316. Currently, the only target I know about that will benefit from this change is UEFI.

This PR can also be used to implement more efficient `Command::output` since the intermediate `Process` is not actually needed anymore, but that is outside the scope of this PR.

Since this is not a public API change, I'm not sure if an RFC is needed or not.

…rk-Simulacrum

bootstrap: Allow installing `llvm-tools`

This PR allows installing the `llvm-tools` dist tarball using `./x.py install`.

…n, r=GuillaumeGomez

rustdoc: clean up margin CSS for scraped examples

* This stops applying a margin to the additional example links. Because these links are `display: inline`, it doesn't actually do anything.
* This switches from using a margin-bottom with a special exception for the examples themselves, plus an additional margin on the hide button, to instead using just margin-top on the examples, with an exception for the first one.

No user-visible changes should result from this.

…illaumeGomez

docs: add long error explanation for error E0320

Continuation of rust-lang#105791

r? ``@GuillaumeGomez``

…-obk

Support call and drop terminators in custom mir

The only caveat with this change is that cleanup blocks are not supported. I would like to add them, but it's not quite clear to me what the best way to do that is, so I'll have to think about it some more.

r? ``@oli-obk``

Speed up tidy

This can be reviewed commit by commit since they contain separate optimizations.

```
# master
$ taskset -c 0-5 hyperfine './x test tidy'
Benchmark #1: ./x test tidy
  Time (mean ± σ):      4.857 s ±  0.064 s    [User: 12.967 s, System: 2.014 s]
  Range (min … max):    4.779 s …  4.997 s    10 runs

# PR
$ taskset -c 0-5 hyperfine './x test tidy'
Benchmark #1: ./x test tidy
  Time (mean ± σ):      3.672 s ±  0.035 s    [User: 10.524 s, System: 2.029 s]
  Range (min … max):    3.610 s …  3.725 s    10 runs
```

…k-Simulacrum

std::fmt: Use args directly in example code

The lint "clippy::uninlined_format_args" recommends inline variables in format strings. Fix two places in the docs that do not do this. I noticed this because I copy/pasted one example in to my project, then noticed this lint error. This fixes:

```
error: variables can be used directly in the `format!` string
  --> src/main.rs:30:22
   |
30 |         let string = format!("{:.*}", decimals, magnitude);
   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: variables can be used directly in the `format!` string
  --> src/main.rs:39:2
   |
39 |  write!(&mut io::stdout(), "{}", args).unwrap();
```