Improve contrast of foreground line number.

CDB doesn't care that you're using static_cast between unrelated types.
VS(C) does.  These should've been reinterpret_cast or C casts.
Cast is from e.g. `u8*` to `tuple<$T1, $T2>*`

…_since, r=jyn514

Make duration_since documentation more clear

…bility, r=nikomatsakis

remove public visibility previously needed for rustfmt

`submod_path_from_attr` in rustc_expand::module was previously public because it was also consumed by rustfmt. However, we've done a bit of refactoring in rustfmt and no longer need to use this function.

This changes the visibility to the parent mod as was originally going to be done before the rustfmt dependency was realized (rust-lang@c189565#diff-cd1b379893bae95f7991d5a3f3c6d337R201)

Improve ayu doc source line number contrast

Improve contrast of foreground line number.

Before

![image](https://user-images.githubusercontent.com/4687791/92305696-1bf2ab80-efbc-11ea-8b5c-a24c4f6261e0.png)

After

![image](https://user-images.githubusercontent.com/4687791/92305700-2a40c780-efbc-11ea-9061-dbfcb1e71980.png)

r? @Cldfire

I think we should add the line for light and dark theme too, it looks better and clearer that way.

…crum

rustbuild: Remove `Mode::Codegen`

It's no longer used.

…, r=petrochenkov

Fix HashMap visualizers in Visual Studio (Code)

CDB (as used in unit tests) doesn't care that we're using static_cast between unrelated types (`u8*` to `tuple<$T1, $T2>*`).
Visual Studio & Visual Studio Code care.  These should've been reinterpret_cast or C casts.

Credit to @petrochenkov per rust-lang#76352 for helping catch this.

### Testing

```cmd
x.py test --stage 1 src/tools/tidy
x.py test --stage 1 --build x86_64-pc-windows-msvc src\test\debuginfo
```

…mplate, r=jonas-schievink

Fix typo in tracking issue template

Add help note to unconstrained const parameter

Resolves rust-lang#68366, since it is currently intended behaviour.
If demonstrating `T -> U` is injective, there should be an additional word that it is not **yet** supported.

r? @lcnr

Update linker-plugin-lto.md to contain up to rust 1.46

Hi,
this is the same as rust-lang#72290, if anyone has suggestions on how to automate this please say :)
otherwise, you can check the versions I've added via:

```sh
$ rustup install 1.44.0
$ rustc +1.44.0 -Vv
rustc 1.44.0 (49cae55 2020-06-01)
binary: rustc
commit-hash: 49cae55
commit-date: 2020-06-01
host: x86_64-unknown-linux-gnu
release: 1.44.0
LLVM version: 9.0

$ rustup install 1.45.0
$ rustc +1.45.0 -Vv
rustc 1.45.0 (5c1f21c 2020-07-13)
binary: rustc
commit-hash: 5c1f21c
commit-date: 2020-07-13
host: x86_64-unknown-linux-gnu
release: 1.45.0
LLVM version: 10.0

$ rustup install 1.46.0
$ rustc +stable -Vv
rustc 1.46.0 (04488af 2020-08-24)
binary: rustc
commit-hash: 04488af
commit-date: 2020-08-24
host: x86_64-unknown-linux-gnu
release: 1.46.0
LLVM version: 10.0
```

Fix documentation for TyCtxt::all_impls

`TyCtxt::all_impls` documentation was wrong about the return type.

Update cargo

8 commits in 126907a7cfccbe93778530e6a6bbaa3adb6c515c..875e0123259b0b6299903fe4aea0a12ecde9324f
2020-08-31 20:42:11 +0000 to 2020-09-08 20:17:21 +0000
- Lowercase and remove periods in error messages for consistency (rust-lang/cargo#8655)
- Allow running build-man.sh from any directory (rust-lang/cargo#8682)
- docs: add details for cargo check pass where cargo build fail (rust-lang/cargo#8677)
- Fix nightly exported_priv_warning test. (rust-lang/cargo#8678)
- fix mdbook test with ```ignore/text/sh/console (rust-lang/cargo#8674)
- End CACHEDIR.TAG with newline (rust-lang/cargo#8672)
- Fixed the fossil repo initialization actually run commands (rust-lang/cargo#8671)
- Remove asciidoc attribute in cargo-metadata man page. (rust-lang/cargo#8670)