Currently, the panic!() calls directly borrow the value bindings. This
causes those bindings to always be initialized, i.e. they're initialized
even before the values are even compared. This causes noticeable
overhead in what should be a really cheap operation.

By performing a reborrow of the value in the call to panic!(), we allow
LLVM to optimize that code, so that the extra borrow only happens in the
error case.

We could achieve the same result by dereferencing the values passed to
panic!(), as the format machinery borrows them anyway, but this causes
assertions to fail to compile if one of the values is unsized, i.e. it
would be a breaking change.

Examples:

```rust
let next_error_type_a = err
    .iter_chain()
    .filter_map(Error::downcast_ref::<ErrorTypeA>)
    .next();
```

```rust
let source_root_error = err.iter_chain().last();
```

Credit for the ErrorIter goes to Tim Diekmann
https://www.reddit.com/r/rust/comments/aj3lpg/is_an_iterator_impl_over_errorsource_possible/

The Ubuntu keyserver is more reliable than the MIT PGP server, which is
prone to going down. This commit also explicitly uses port 80 on the
keyserver for reasons outlined in rust-lang#57844.

These macros are not required to glue the `core_arch` crate anymore.

Doc rewording

None

Speed up the fast path for assert_eq! and assert_ne!

Currently, the panic!() calls directly borrow the value bindings. This
causes those bindings to always be initialized, i.e. they're initialized
even before the values are even compared. This causes noticeable
overhead in what should be a really cheap operation.

By performing a reborrow of the value in the call to panic!(), we allow
LLVM to optimize that code, so that the extra borrow only happens in the
error case.

We could achieve the same result by dereferencing the values passed to
panic!(), as the format machinery borrows them anyway, but this causes
assertions to fail to compile if one of the values is unsized, i.e. it
would be a breaking change.

…=alexcrichton

Stabilize the time_checked_add feature

Closes rust-lang#55940

Stabilizes `checked_add` and `checked_sub` on `Instant` and `SystemTime`.

…alexcrichton

Stabilize linker-plugin based LTO (aka cross-language LTO)

This PR stabilizes [linker plugin based LTO](rust-lang#49879), also known as "cross-language LTO" because it allows for doing inlining and other optimizations across language boundaries in mixed Rust/C/C++ projects.

As described in the tracking issue, it works by making `rustc` emit LLVM bitcode instead of machine code, the same as `clang` does. A linker with the proper plugin (like LLD) can then run (Thin)LTO across all modules.

The feature has been implemented over a number of pull requests and there are various [codegen](https://github.com/rust-lang/rust/blob/master/src/test/codegen/no-dllimport-w-cross-lang-lto.rs) and [run](https://github.com/rust-lang/rust/tree/master/src/test/run-make-fulldeps/cross-lang-lto-clang)-[make](https://github.com/rust-lang/rust/tree/master/src/test/run-make-fulldeps/cross-lang-lto-upstream-rlibs) [tests](https://github.com/rust-lang/rust/tree/master/src/test/run-make-fulldeps/cross-lang-lto) that make sure that it keeps working.

It also works for building big projects like [Firefox](https://treeherder.mozilla.org/#/jobs?repo=try&revision=2ce2d5ddcea6fbff790503eac406954e469b2f5d).

The PR makes the feature available under the `-C linker-plugin-lto` flag. As discussed in the tracking issue it is not cross-language specific and also not LLD specific. `-C linker-plugin-lto` is descriptive of what it does. If someone has a better name, let me know `:)`

Add FreeBSD armv6 and armv7 targets

…stebank

Cleanup: rename node_id_to_type(_opt)

Renames `node_id_to_type(_opt)` to `hir_id_to_type(_opt)`; this makes it clear we are dealing with HIR nodes and their IDs here.

In addition, a drive-by commit removing `ty::item_path::hir_path_str` (as requested by @eddyb).

…rochenkov

allow shorthand syntax for deprecation reason

Fixes rust-lang#48271.

Created based on discussion in rust-lang#56896.

… r=oli-obk

Add specific feature gate error for const-unstable features

Before:
```
error: `impl Trait` in const fn is unstable
 --> src/lib.rs:7:19
  |
7 | const fn foo() -> impl T {
  |                   ^^^^^^

error: aborting due to previous error
```

After:
```
error[E0723]: `impl Trait` in const fn is unstable (see issue rust-lang#57563)
 --> src/lib.rs:7:19
  |
7 | const fn foo() -> impl T {
  |                   ^^^^^^
  = help: add #![feature(const_fn)] to the crate attributes to enable

error: aborting due to previous error
```

This improves the situation with rust-lang#57563. Fixes rust-lang#57544. Fixes rust-lang#54469.

r? @oli-obk

fix str mutating through a ptr derived from &self

Found by Miri: In `get_unchecked_mut` (also used by the checked variants internally) uses `str::as_ptr` to create a mutable reference, but `as_ptr` takes `&self`.  This means the mutable references we return here got created from a shared reference, which violates the shared-references-are-read-only discipline!

For this by using a newly introduced `as_mut_ptr` instead.

…wjasper

Rename rustc_errors dependency in rust 2018 crates

I think this is a better solution than `use rustc_errors as errors` in `lib.rs` and `use crate::errors` in modules.

Related: rust-lang/cargo#5653

cc rust-lang#58099

r? @Centril

impl iter() for dyn Error

Examples:

```rust
let next_error_type_a = err
    .iter()
    .filter_map(Error::downcast_ref::<ErrorTypeA>)
    .next();
```

```rust
let source_root_error = err.iter().last();
```

Credit for the ErrorIter goes to reddit user /u/tdiekmann (Tim Diekmann)
https://www.reddit.com/r/rust/comments/aj3lpg/is_an_iterator_impl_over_errorsource_possible/

…ichton

use Ubuntu keyserver for CloudABI ports

The Ubuntu keyserver is more reliable than the MIT PGP server, which is
prone to going down. This commit also explicitly uses port 80 on the
keyserver for reasons outlined in rust-lang#57844.

…crichton

Remove some dead code from libcore

These macros are not required to glue the `core_arch` crate anymore.