`file_metadata_raw` interns the strings `"<unknown>"` and `""` very
frequently. This commit avoids that, which reduces the number of symbols
interned significantly and reduces instruction counts by up to 0.5% on
some workloads.

`find_attr_val(&line, "since")` returns `Some(", issue = ")` when
`line` is set to the following line:

```
[unstable(feature = "checked_duration_since", issue = "58402")]
```

Make `find_attr_val` use regex that is a little bit more
precise (requires `=` after key name).

It still does not handle all cases (e.g., extra leading chars in key
name, or escaped quotes in value), but is good enough for now.

Make deprecation lint `ambiguous_associated_items` deny-by-default

As requested by r? @Centril

cc rust-lang#57644

Added arm-none-eabi target

Hello,

This PR adds a new target for compiling bare-metal ARM Cortex-A programs.

I've managed to build and use this new target, but I am unclear with regards to a few details:

- I'm not sure what are the criteria for choosing between lld and gnu-ld
- When trying to build with `./x.py build --target arm-none-eabi`, the script tries to compile with `cc`, instead of `arm-none-eabi-gcc`. It could find different cross-compilers just fine, but I didn't understand where I had to specify it. (I ended up specifying `CC_arm_none_eabi=arm-none-eabi-gcc` in the environment).
- I couldn't find where I can exclude std from compiling for this target (as I guess occurs with other bare-metal targets).
- Should I add a separate target for `eabihf`?

…rrors, r=QuietMisdreavus

report fatal errors during doctest parsing

Fixes rust-lang#59557.

… r=Centril

Tidy: ensure lang features are sorted by since

This is the tidy side of rust-lang#60361.

What is left is actually splitting features into groups and sorting by since.

This PR also likely to produce a small (a couple of lines) merge conflict with rust-lang#60362.

r? @Centril

 Do not suggest incorrect syntax on pattern type error due to borrow

Fix rust-lang#55174.

Rename `RUST_LOG` to `RUSTC_LOG`

cc: rust-lang#57985

I think we should also change these submodules:

- rustc-guide
- Cargo (rename to `CARGO_LOG`, cc: rust-lang/cargo#6605)
- miri
- rls
- rustfmt

r? @davidtwco

…e, r=oli-obk

Require a trait in the bounds of existential types

Fixes rust-lang#53090

r? @oli-obk

…r=pnkfelix

Constrain all regions in the concrete type for an opaque type

`push_outlives_components` skips some regions in a type, notably the signature
of a closure is ignored. Most of the time this is OK, but for opaque types the
concrete type is used when checking auto-trait bounds in other functions.

cc @nikomatsakis @pnkfelix

Closes rust-lang#57464
Closes rust-lang#60127

…vidtwco

Resolve match arm ty when arms diverge

Fix rust-lang#58695.

… r=oli-obk

Const prop refactoring

This is rebased on top of rust-lang#60428 so only the top commit is new.

This is the refactoring to remove the `mir` field from `ConstPropagator` which is necessary before we can begin to actually propagate constants.

r? @oli-obk

…r=davidtwco

Avoid repeated interning of static strings.

`file_metadata_raw` interns the strings `"<unknown>"` and `""` very
frequently. This commit avoids that, which reduces the number of symbols
interned significantly and reduces instruction counts by up to 0.5% on
some workloads.