This is needed to match MIR more conservative approximation of any
borrowed value being live across a suspend point (See rust-lang#94067). This
change considers an expression such as `x.y = z` to be a borrow of `x`
and therefore keeps `x` live across suspend points.

Previously it would be skipped if codegen-backends doesn't contain llvm.

As an example:

    #[test]
    #[ignore = "not yet implemented"]
    fn test_ignored() {
        ...
    }

Will now render as:

    running 2 tests
    test tests::test_ignored ... ignored, not yet implemented

    test result: ok. 1 passed; 0 failed; 1 ignored; 0 measured; 0 filtered out; finished in 0.00s

rustfmt doesn't format `let ... else`.

…ulacrum

Provide ignore message in the result of test

Provide ignore the message in the result of the test.

This PR does not need RFC, because it is about the presentation of the report of `cargo test`.

However, the following document listed here helps you to know about PR.

- [RFC](rust-lang/rfcs#3217)
- [Rendered](https://github.com/yanganto/rfcs/blob/ignore-test-message/text/0000-ignore-test-message.md)
- [Previous discussion on IRLO](https://internals.rust-lang.org/t/pre-rfc-provide-ignore-message-when-the-test-ignored/15904)

If there is something improper, please let me know.
Thanks.

…rk-Simulacrum

Always check cg_llvm with ./x.py check

Previously it would be skipped if codegen-backends doesn't contain llvm.

…andry

Consider mutations as borrows in generator drop tracking

This is needed to match MIR more conservative approximation of any borrowed value being live across a suspend point (See rust-lang#94067). This change considers an expression such as `x.y = z` to be a borrow of `x` and therefore keeps `x` live across suspend points.

r? `@nikomatsakis`

BTree: simplify test code

Mostly, use `from` & `from_iter`.

update const_generics_defaults release notes

supersedes rust-lang#94294

r? `@Mark-Simulacrum`

Remove a duplicate space

rustfmt doesn't format `let ... else`.