…iaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#123480 (deref patterns: impl `DerefPure` for more std types)
 - rust-lang#124412 (io safety: update Unix explanation to use `Arc`)
 - rust-lang#124441 (String.truncate comment microfix (greater or equal))
 - rust-lang#124594 (run-make-support: preserve tooks.mk behavior for EXTRACXXFLAGS)
 - rust-lang#124604 (library/std: Remove unused `gimli-symbolize` feature)
 - rust-lang#124607 (`rustc_expand` cleanups)
 - rust-lang#124609 (variable-precision float operations can differ depending on optimization levels)
 - rust-lang#124610 (Tweak `consts_may_unify`)
 - rust-lang#124626 (const_eval_select: add tracking issue)
 - rust-lang#124637 (AST pretty: Use `builtin_syntax` for type ascription)

Failed merges:

 - rust-lang#124638 (Move some tests from `rustc_expand` to `rustc_parse`.)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#123480 - Nadrieril:impl-all-derefpures, r=compiler-errors

deref patterns: impl `DerefPure` for more std types

Context: [deref patterns](rust-lang#87121). The requirements of `DerefPure` aren't precise yet, but these types unambiguously satisfy them.

Interestingly, a hypothetical `impl DerefMut for Cow` that does a `Clone` would *not* be eligible for `DerefPure` if we allow mixing deref patterns with normal patterns. If the following is exhaustive then the `DerefMut` would cause UB:
```rust
match &mut Cow::Borrowed(&()) {
    Cow::Owned(_) => ..., // Doesn't match
    deref!(_x) if false => ..., // Causes the variant to switch to `Owned`
    Cow::Borrowed(_) => ..., // Doesn't match
    // We reach unreachable
}
```