… r=Manishearth

Stablize `non-ascii-idents`

This is the stablization PR for RFC 2457. Currently this is waiting on fcp in [tracking issue](rust-lang#55467).

r? `@Manishearth`

Pkgsrc changes:
 * Bump bootstrap requirements to 1.52.1
 * Adjust patches, adapt to upstream changes, adjust cargo checksums
 * If using an external llvm, require >= 10.0

Upsteream changes:

Version 1.53.0 (2021-06-17)
============================

Language
-----------------------
- [You can now use unicode for identifiers.][83799] This allows
  multilingual identifiers but still doesn't allow glyphs that are
  not considered characters such as `#` (diamond) or `<U 1F980>`
  (crab). More specifically you can now use any identifier that
  matches the UAX #31 "Unicode Identifier and Pattern Syntax" standard. This
  is the same standard as languages like Python, however Rust uses NFC
  normalization which may be different from other languages.
- [You can now specify "or patterns" inside pattern matches.][79278]
  Previously you could only use `|` (OR) on complete patterns. E.g.
  ```rust
  let x = Some(2u8);
  // Before
  matches!(x, Some(1) | Some(2));
  // Now
  matches!(x, Some(1 | 2));
  ```
- [Added the `:pat_param` `macro_rules!` matcher.][83386] This matcher
  has the same semantics as the `:pat` matcher. This is to allow `:pat`
  to change semantics to being a pattern fragment in a future edition.

Compiler
-----------------------
- [Updated the minimum external LLVM version to LLVM 10.][83387]
- [Added Tier 3\* support for the `wasm64-unknown-unknown` target.][80525]
- [Improved debuginfo for closures and async functions on Windows MSVC.][83941]

\* Refer to Rust's [platform support page][platform-support-doc] for more
information on Rust's tiered platform support.

Libraries
-----------------------
- [Abort messages will now forward to `android_set_abort_message` on
  Android platforms when available.][81469]
- [`slice::IterMut<'_, T>` now implements `AsRef<[T]>`][82771]
- [Arrays of any length now implement `IntoIterator`.][84147]
  Currently calling `.into_iter()` as a method on an array will
  return `impl Iterator<Item=&T>`, but this may change in a
  future edition to change `Item` to `T`. Calling `IntoIterator::into_iter`
  directly on arrays will provide `impl Iterator<Item=T>` as expected.
- [`leading_zeros`, and `trailing_zeros` are now available on all
  `NonZero` integer types.][84082]
- [`{f32, f64}::from_str` now parse and print special values
  (`NaN`, `-0`) according to IEEE RFC 754.][78618]
- [You can now index into slices using `(Bound<usize>, Bound<usize>)`.][77704]
- [Add the `BITS` associated constant to all numeric types.][82565]

Stabilised APIs
---------------
- [`AtomicBool::fetch_update`]
- [`AtomicPtr::fetch_update`]
- [`BTreeMap::retain`]
- [`BTreeSet::retain`]
- [`BufReader::seek_relative`]
- [`DebugStruct::non_exhaustive`]
- [`Duration::MAX`]
- [`Duration::ZERO`]
- [`Duration::is_zero`]
- [`Duration::saturating_add`]
- [`Duration::saturating_mul`]
- [`Duration::saturating_sub`]
- [`ErrorKind::Unsupported`]
- [`Option::insert`]
- [`Ordering::is_eq`]
- [`Ordering::is_ge`]
- [`Ordering::is_gt`]
- [`Ordering::is_le`]
- [`Ordering::is_lt`]
- [`Ordering::is_ne`]
- [`OsStr::is_ascii`]
- [`OsStr::make_ascii_lowercase`]
- [`OsStr::make_ascii_uppercase`]
- [`OsStr::to_ascii_lowercase`]
- [`OsStr::to_ascii_uppercase`]
- [`Peekable::peek_mut`]
- [`Rc::decrement_strong_count`]
- [`Rc::increment_strong_count`]
- [`Vec::extend_from_within`]
- [`array::from_mut`]
- [`array::from_ref`]
- [`char::MAX`]
- [`char::REPLACEMENT_CHARACTER`]
- [`char::UNICODE_VERSION`]
- [`char::decode_utf16`]
- [`char::from_digit`]
- [`char::from_u32_unchecked`]
- [`char::from_u32`]
- [`cmp::max_by_key`]
- [`cmp::max_by`]
- [`cmp::min_by_key`]
- [`cmp::min_by`]
- [`f32::is_subnormal`]
- [`f64::is_subnormal`]

Cargo
-----------------------
- [Cargo now supports git repositories where the default `HEAD` branch is not
  "master".][cargo/9392] This also includes a switch to the version
  3 `Cargo.lock` format which can handle default branches correctly.
- [macOS targets now default to `unpacked` split-debuginfo.][cargo/9298]
- [The `authors` field is no longer included in `Cargo.toml` for new
  projects.][cargo/9282]

Rustdoc
-----------------------
- [Added the `rustdoc::bare_urls` lint that warns when you have URLs
  without hyperlinks.][81764]

Compatibility Notes
-------------------
- [Implement token-based handling of attributes during expansion][82608]
- [`Ipv4::from_str` will now reject octal format IP addresses in addition
  to rejecting hexadecimal IP addresses.][83652] The octal format can lead
  to confusion and potential security vulnerabilities and [is no
  longer recommended][ietf6943].

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [Rework the `std::sys::windows::alloc` implementation.][83065]
- [rustdoc: Don't enter an infer_ctxt in get_blanket_impls for
  impls that aren't blanket impls.][82864]
- [rustdoc: Only look at blanket impls in `get_blanket_impls`][83681]
- [Rework rustdoc const type][82873]

[83386]: rust-lang/rust#83386
[82771]: rust-lang/rust#82771
[84147]: rust-lang/rust#84147
[84082]: rust-lang/rust#84082
[83799]: rust-lang/rust#83799
[83681]: rust-lang/rust#83681
[83652]: rust-lang/rust#83652
[83387]: rust-lang/rust#83387
[82873]: rust-lang/rust#82873
[82864]: rust-lang/rust#82864
[82608]: rust-lang/rust#82608
[82565]: rust-lang/rust#82565
[80525]: rust-lang/rust#80525
[79278]: rust-lang/rust#79278
[78618]: rust-lang/rust#78618
[77704]: rust-lang/rust#77704
[83941]: rust-lang/rust#83941
[83065]: rust-lang/rust#83065
[81764]: rust-lang/rust#81764
[81469]: rust-lang/rust#81469
[cargo/9298]: rust-lang/cargo#9298
[cargo/9282]: rust-lang/cargo#9282
[cargo/9392]: rust-lang/cargo#9392
[`char::MAX`]: https://doc.rust-lang.org/std/primitive.char.html#associatedconstant.MAX
[`char::REPLACEMENT_CHARACTER`]: https://doc.rust-lang.org/std/primitive.char.html#associatedconstant.REPLACEMENT_CHARACTER
[`char::UNICODE_VERSION`]: https://doc.rust-lang.org/std/primitive.char.html#associatedconstant.UNICODE_VERSION
[`char::decode_utf16`]: https://doc.rust-lang.org/std/primitive.char.html#method.decode_utf16
[`char::from_u32`]: https://doc.rust-lang.org/std/primitive.char.html#method.from_u32
[`char::from_u32_unchecked`]: https://doc.rust-lang.org/std/primitive.char.html#method.from_u32_unchecked
[`char::from_digit`]: https://doc.rust-lang.org/std/primitive.char.html#method.from_digit
[`AtomicBool::fetch_update`]: https://doc.rust-lang.org/std/sync/atomic/struct.AtomicBool.html#method.fetch_update
[`AtomicPtr::fetch_update`]: https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html#method.fetch_update
[`BTreeMap::retain`]: https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#method.retain
[`BTreeSet::retain`]: https://doc.rust-lang.org/std/collections/struct.BTreeSet.html#method.retain
[`BufReader::seek_relative`]: https://doc.rust-lang.org/std/io/struct.BufReader.html#method.seek_relative
[`DebugStruct::non_exhaustive`]: https://doc.rust-lang.org/std/fmt/struct.DebugStruct.html#method.finish_non_exhaustive
[`Duration::MAX`]: https://doc.rust-lang.org/std/time/struct.Duration.html#associatedconstant.MAX
[`Duration::ZERO`]: https://doc.rust-lang.org/std/time/struct.Duration.html#associatedconstant.ZERO
[`Duration::is_zero`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.is_zero
[`Duration::saturating_add`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.saturating_add
[`Duration::saturating_mul`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.saturating_mul
[`Duration::saturating_sub`]: https://doc.rust-lang.org/std/time/struct.Duration.html#method.saturating_sub
[`ErrorKind::Unsupported`]: https://doc.rust-lang.org/std/io/enum.ErrorKind.html#variant.Unsupported
[`Option::insert`]: https://doc.rust-lang.org/std/option/enum.Option.html#method.insert
[`Ordering::is_eq`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.is_eq
[`Ordering::is_ge`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.is_ge
[`Ordering::is_gt`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.is_gt
[`Ordering::is_le`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.is_le
[`Ordering::is_lt`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.is_lt
[`Ordering::is_ne`]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.is_ne
[`OsStr::eq_ignore_ascii_case`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.eq_ignore_ascii_case
[`OsStr::is_ascii`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.is_ascii
[`OsStr::make_ascii_lowercase`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.make_ascii_lowercase
[`OsStr::make_ascii_uppercase`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.make_ascii_uppercase
[`OsStr::to_ascii_lowercase`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.to_ascii_lowercase
[`OsStr::to_ascii_uppercase`]: https://doc.rust-lang.org/std/ffi/struct.OsStr.html#method.to_ascii_uppercase
[`Peekable::peek_mut`]: https://doc.rust-lang.org/std/iter/struct.Peekable.html#method.peek_mut
[`Rc::decrement_strong_count`]: https://doc.rust-lang.org/std/rc/struct.Rc.html#method.increment_strong_count
[`Rc::increment_strong_count`]: https://doc.rust-lang.org/std/rc/struct.Rc.html#method.increment_strong_count
[`Vec::extend_from_within`]: https://doc.rust-lang.org/beta/std/vec/struct.Vec.html#method.extend_from_within
[`array::from_mut`]: https://doc.rust-lang.org/beta/std/array/fn.from_mut.html
[`array::from_ref`]: https://doc.rust-lang.org/beta/std/array/fn.from_ref.html
[`cmp::max_by_key`]: https://doc.rust-lang.org/beta/std/cmp/fn.max_by_key.html
[`cmp::max_by`]: https://doc.rust-lang.org/beta/std/cmp/fn.max_by.html
[`cmp::min_by_key`]: https://doc.rust-lang.org/beta/std/cmp/fn.min_by_key.html
[`cmp::min_by`]: https://doc.rust-lang.org/beta/std/cmp/fn.min_by.html
[`f32::is_subnormal`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_subnormal
[`f64::is_subnormal`]: https://doc.rust-lang.org/std/primitive.f64.html#method.is_subnormal
[ietf6943]: https://datatracker.ietf.org/doc/html/rfc6943#section-3.1.1