Replace the ICEing on const fn loops with an error

fixes #56035

Forward rust version number to tools

Clippy uses it to identify the correct documentation to point to

cc @Manishearth @nrc

sibling PR in clippy: https://github.com/rust-lang-nursery/rust-clippy/pull/3442

Update books for Rust 2018

This PR:

1. updates all of the books
    * I don't know if @Gankro has further plans for the nomicon or not
2. updates the build process because TRPL is only distributing one edition now
3. fixes up the stdlib links

I think that this passes but it's 3:20 am and so I'm sending it in and will fix up anything i missed in the morning.

/cc @alexcrichton for the big beta backport

Clippy uses it to identify the correct documentation to point to

resolve: Make "empty import canaries" invisible from other crates

Empty imports `use prefix::{};` are desugared into `use prefix::{self as _};` to make sure the prefix is checked for privacy/stability/etc.
This caused issues in cross-crate scenarios because gensyms are lost in crate metadata (the `_` is a gensym).

Fixes https://github.com/rust-lang/rust/issues/55811

rustc: remove {FxHash,Node,DefId,HirId,ItemLocal}{Map,Set} "constructor" fns.

These are cruft left over from a time when `Foo::default()` didn't "just work".

Stabilize `extern_crate_item_prelude`

Closes https://github.com/rust-lang/rust/issues/55599

Update RLS and Rustfmt

Re-opening https://github.com/rust-lang/rust/pull/56061

@bors: r=kennytm p=2

Make const_eval_raw query return just an AllocId

r? @oli-obk

Allow #[must_use] on traits

Addresses https://github.com/rust-lang/rust/issues/55506, but we'll probably want to add it to some library traits like `Iterator` before the issue is considered fixed. Fixes https://github.com/rust-lang/rust/issues/51560.

`#[must_use]` is already permitted on traits, with no effect, so this seems like a bug fix, but I might be overlooking something. This currently warns for `impl Trait` or `dyn Trait` when the `Trait` is `#[must_use]` (although I don't think the latter is currently possible, so it's simply future-proofed).

Updated RELEASES.md for 1.31.0

[Rendered](https://github.com/Aaronepower/rust/blob/master/RELEASES.md)

r? @Mark-Simulacrum

cc @rust-lang/release

Add temporary renames to manifests for rustfmt/clippy

This will be part of our strategy for shipping renamed versions of these
components for the Rust 2018 edition.

Closes #55967

Fix stability hole with `static _`

The `underscore_const_names` only gated const items with `_` as the name.

`static _: () = ();` works on beta without feature gates right now, this PR fixes that.

Revert #51601

Closes: #55985

Specialization of `StepBy<Range(Inclusive)>` results in an incorrectly behaving code when `step_by` is combined with `skip` or `nth`.

If this will get merged we probably should reopen issues previously closed by #51601 (if there was any).

This will be part of our strategy for shipping renamed versions of these
components for the Rust 2018 edition.

Closes #55967

Ignore non-semantic tokens for 'probably_eq' streams.

Improves the situation in #43081 by skipping typically non-semantic tokens when checking for 'probably_eq'.

r? @alexcrichton

save-analysis: fallback to using path id

r? @EddyB

Rollup of 25 pull requests

Successful merges:

 - #55562 (Add powerpc- and powerpc64-unknown-linux-musl targets)
 - #55564 (test/linkage-visibility: Ignore on musl targets)
 - #55827 (A few tweaks to iterations/collecting)
 - #55834 (Forward the ABI of the non-zero sized fields of an union if they have the same ABI)
 - #55857 (remove unused dependency)
 - #55862 (in which the E0618 "expected function" diagnostic gets a makeover)
 - #55867 (do not panic just because cargo failed)
 - #55894 (miri enum discriminant handling: Fix treatment of pointers, better error when it is undef)
 - #55916 (Make miri value visitor useful for mutation)
 - #55919 (core/tests/num: Simplify `test_int_from_str_overflow()` test code)
 - #55923 (reword #[test] attribute error on fn items)
 - #55949 (ty: return impl Iterator from Predicate::walk_tys)
 - #55952 (Update to Clang 7 on CI.)
 - #55953 (#53488 Refactoring UpvarId)
 - #55962 (rustdoc: properly calculate spans for intra-doc link resolution errors)
 - #55963 (Stress test for MPSC)
 - #55968 (Clean up some non-mod-rs stuff.)
 - #55970 (Miri backtrace improvements)
 - #56007 (CTFE: dynamically make sure we do not call non-const-fn)
 - #56011 (Replace data.clone() by Arc::clone(&data) in mutex doc.)
 - #56012 (avoid shared ref in UnsafeCell::get)
 - #56016 (Add VecDeque::resize_with)
 - #56027 (docs: Add missing backtick in object_safety.rs docs)
 - #56043 (remove "approx env bounds" if we already know from trait)
 - #56059 (Increase `Duration` approximate equal threshold to 1us)

Increase `Duration` approximate equal threshold to 1us

Previously this threshold when testing was 100ns, but the Windows
documentation states:

> which is a high resolution (<1us) time stamp

which presumably means that we could have up to 1us resolution, which
means that 100ns doesn't capture "equivalent" time intervals due to
various bits of rounding here and there.

It's hoped that this..

Closes #56034