This was already only enabled in debug_assertions builds. Generally, it seems
like most use cases that would use this could also use the -Zself-profile flag
which also tracks cache hits (in all builds), and so the extra cfg's and such
are not really necessary.

This is largely just a small cleanup though, which primarily is intended to make
other changes easier by avoiding the need to deal with this field.

A continuation of rust-lang#89718.

to avoid relying on the discriminant of the former for FFI purposes

…ons, r=joshtriplett

Add #[must_use] to as_type conversions

Clippy missed these:

```rust
alloc::string::String   fn as_mut_str(&mut self) -> &mut str;
core::mem::NonNull<T>   unsafe fn as_uninit_mut<'a>(&mut self) -> &'a MaybeUninit<T>;
str                     unsafe fn as_bytes_mut(&mut self) -> &mut [u8];
str                     fn as_mut_ptr(&mut self) -> *mut u8;
```

Parent issue: rust-lang#89692

r? ````@joshtriplett````

…acking, r=petrochenkov

Remove built-in query cache_hit tracking

This was already only enabled in debug_assertions builds. Generally, it seems
like most use cases that would use this could also use the -Zself-profile flag
which also tracks cache hits (in all builds), and so the extra cfg's and such
are not really necessary.

This is largely just a small cleanup though, which primarily is intended to make
other changes easier by avoiding the need to deal with this field.

…b-methods, r=joshtriplett

Add #[must_use] to non-mutating verb methods

These are methods that could be misconstrued to mutate their input, similar to rust-lang#89694. I gave each one a different custom message.

I wrote that `upgrade` and `downgrade` don't modify the input pointers. Logically they don't, but technically they do...

Parent issue: rust-lang#89692

r? ```@joshtriplett```

…ts, r=joshtriplett

Add #[must_use] to is_condition tests

I threw in `std::path::Path::has_root` for funsies.

A continuation of rust-lang#89718.

Parent issue: rust-lang#89692

r? ```@joshtriplett```

…htriplett

fix minor spelling error in Poll::ready docs

Fixes minor spelling error in the proposed `Poll::ready` docs. Not that my opinion matters, but +1 on the original PR (rust-lang#89651), it reads much nicer to me than the `ready!` macro.

Update books

## nomicon

5 commits in 2747c4bb2cbc0639b733793ddb0bf4e9daa2634e..2d66852a27c5d0ec50ae021820d1de22caa2b1bd
2021-09-19 17:33:32 +0900 to 2021-10-07 19:00:37 +0900
- Fix typo/minor grammar error in subtyping.md (rust-lang/nomicon#317)
- doc: clarify `thread::scoped::JoinGuard` chapter (rust-lang/nomicon#313)
- Clarify niche optimization on enums with reprs (rust-lang/nomicon#315)
- Update rc decrement snipped (rust-lang/nomicon#316)
- Remove useless `unsafe`, `mut` and ptr casts in example in `send-and-sync.md` (rust-lang/nomicon#308)

## reference

2 commits in 13747275bd14c2d2b453100498532f9ae5504769..b5c68b02984f74e99d1f1b332029e05f607e2660
2021-09-24 17:44:04 +0900 to 2021-10-02 08:11:35 -0700
- Use subtrait/supertrait, not sub-trait, super-trait. (rust-lang/reference#1095)
- Fixed link typo in Generics.md (rust-lang/reference#1094)

## rust-by-example

3 commits in 28aca4a36962c709bce301c03114b5589381dfb8..9a60624fcad0140826c44389571dc622917cd632
2021-09-25 08:19:51 -0300 to 2021-10-04 08:13:53 -0300
- Change 1..n + 1 to 1..=n (rust-lang/rust-by-example#1467)
- Close rust-lang/rust-by-example#1464 (rust-lang/rust-by-example#1465)
- Fix incorrect formatted print hint; closes rust-lang/rust-by-example#1459. (rust-lang/rust-by-example#1466)

## rustc-dev-guide

11 commits in d1f03cbaa39d9164f5fe4b9b93762668142e0dad..fba15a46ca8efa97e8a955794724ac7ce27805b8
2021-09-24 12:00:29 +0900 to 2021-10-12 08:52:21 +0900
- Update some docs from 2021-10 date triage (rust-lang/rustc-dev-guide#1230)
- Recommend `rustfmt --edition=2021`
- Update sanitizer documentation
- Mention needs-sanitizer-hwaddress directive
- Address review comments
- Document tracing awesomeness
- Move log/tracing instructions to its own file
- Update src/closure.md
- Fix accidental HTML tag
- Update links to `rustc_mir` in Two Phase Borrows (rust-lang/rustc-dev-guide#1226)
- Update some docs from 2021-10 date triage (rust-lang/rustc-dev-guide#1224)

## edition-guide

1 commits in 2d9b1b9da706de24650fdc5c3b0182f55c82115d..7c0088ca744d293a5f4b1e2ac378e7c23d30fe55
2021-08-31 10:44:09 +0200 to 2021-10-05 13:28:05 +0200
- Clarify cargo resolver behavior in a workspace. (rust-lang/edition-guide#267)

## embedded-book

2 commits in 4c76da9ddb4650203c129fceffdea95a3466c205..270fccd339e5972d9c900e788f197e81a0bcd956
2021-09-12 12:43:03 +0000 to 2021-10-06 16:28:48 +0000
- Update section 1.4 to mention that some additional packages required  (rust-embedded/book#304)
- Change `-file-headers` to `--file-headers`  (rust-embedded/book#303)

…haelwoerister

Remap ssa RealPredicate to llvm RealPredicate

to avoid relying on the discriminant of the former for FFI purposes