This commit extends the current unused macro linter
to support directives like #[allow(unused_macros)]
or #[deny(unused_macros)] directly next to the macro
definition, or in one of the modules the macro is
inside. Before, we only supported such directives
at a per crate level, due to the crate's NodeId
being passed to session.add_lint.

We also had to implement handling of the macro's
NodeId in the lint visitor.

Part of rust-lang#29378.

Part of rust-lang#29378 .

- In particular explains *why* we would use the builder instead of
  the free function.
- Changes the parent-child explanation for a spawned-caller.
- Add link to `io::Result` in `thread::Builder`
- Corrects the `thread::Builder::spawn` documentation.

Fixes rust-lang#41568

Make diagnostic note for existing method with unsatisfied trait bounds
multiline for cleaner output.

```
  = note: the method `count` exists but the following trait bounds were not satisfied:
          `[closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`
          `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>> [closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`

Before:

```
  = note: the method `count` exists but the following trait bounds were not satisfied: `[closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`, `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
```

Part of rust-lang#29378 .

…r=arielb1

Make unsatisfied trait bounds note multiline

Make diagnostic note for existing method with unsatisfied trait bounds
multiline for cleaner output.

```
  = note: the method `count` exists but the following trait bounds were not satisfied:
          `[closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`
          `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>> [closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
```

Before:

```
  = note: the method `count` exists but the following trait bounds were not satisfied: `[closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53] : std::ops::FnMut<(&_,)>`, `std::iter::Filter<std::iter::Fuse<std::iter::Once<&str>>, [closure@../../src/test/compile-fail/issue-36053-2.rs:17:39: 17:53]> : std::iter::Iterator`
```

Add lint for unused macros

Addresses parts of rust-lang#34938, to add a lint for unused macros.

We now output warnings by default when we encounter a macro that we didn't use for expansion.

Issues to be resolved before this PR is ready for merge:

- [x] fix the NodeId issue described above
- [x] remove all unused macros from rustc and the libraries or set `#[allow(unused_macros)]` next to them if they should be kept for some reason. This is needed for successful boostrap and bors to accept the PR. -> rust-lang#41934
- [x] ~~implement the full extent of rust-lang#34938, that means the macro match arm checking as well.~~ *let's not do this for now*

Rewrite make-win-dist.py in Rust

Fixes rust-lang#41568

…umeGomez

[Doc] Explain why `thread::yield_now` could be used.

Part of rust-lang#29378.

r? @steveklabnik

…eGomez

[Doc] Implrove `thread::Builder`'s doc.

Part of rust-lang#29378 .

- Explains *why* we would use the builder instead ofthe free function.
- Changes the parent-child explanation for a spawned-caller in `thread::Builder::spawn`
- Adds a link to `io::Result` in `thread::Builder`
- Corrects the return type doc in `thread::Builder::spawn`

r? @rust-lang/docs

[Doc] Add links to the `thread::LocalKey` doc.

Part of rust-lang#29378 .

I do not know exactly what should be done for the `cleanup` part, if you have any idea I'll gladly do it.

r? @rust-lang/docs

…umeGomez

rustdoc: Display `extern "C" fn` instead of `extern fn`

It was decided in rust-lang/style-team#52 to be explicit about the ABI so rustdoc should follow suit.

Fix regression in `macro_rules!` name matching

Fixes rust-lang#41803.
r? @nrc