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)