Pkgsrc changes:
 * Bump bootstrap kit version to 1.51.0.
 * Adjust patches as needed.
 * Update checksum adjustments.
 * Fix syntax error in commands adjusting libserde_derive for Darwin

Upstream changes:

Version 1.52.1 (2021-05-10)
============================

This release disables incremental compilation, unless the user has explicitly
opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable.

This is due to the widespread, and frequently occuring, breakage encountered by
Rust users due to newly enabled incremental verification in 1.52.0. Notably,
Rust users **should** upgrade to 1.52.0 or 1.52.1: the bugs that are detected by
newly added incremental verification are still present in past stable versions,
and are not yet fixed on any channel. These bugs can lead to miscompilation of
Rust binaries.

These problems only affect incremental builds, so release builds with Cargo
should not be affected unless the user has explicitly opted into incremental.
Debug and check builds are affected.

See [84970] for more details.

[84970]: rust-lang/rust#84970

Version 1.52.0 (2021-05-06)
============================

Language
--------
- [Added the `unsafe_op_in_unsafe_fn` lint, which checks whether
  the unsafe code in an `unsafe fn` is wrapped in a `unsafe`
  block.][79208] This lint is allowed by default, and may become
  a warning or hard error in a future edition.

- [You can now cast mutable references to arrays to a pointer of
  the same type as the element.][81479]

Compiler
--------
- [Upgraded the default LLVM to LLVM 12.][81451]

Added tier 3\* support for the following targets.

- [`s390x-unknown-linux-musl`][82166]
- [`riscv32gc-unknown-linux-musl` & `riscv64gc-unknown-linux-musl`][82202]
- [`powerpc-unknown-openbsd`][82733]

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

Libraries
---------
- [`OsString` now implements `Extend` and `FromIterator`.][82121]
- [`cmp::Reverse` now has `#[repr(transparent)]` representation.][81879]
- [`Arc<impl Error>` now implements `error::Error`.][80553]
- [All integer division and remainder operations are now `const`.][80962]

Stabilised APIs
-------------
- [`Arguments::as_str`]
- [`char::MAX`]
- [`char::REPLACEMENT_CHARACTER`]
- [`char::UNICODE_VERSION`]
- [`char::decode_utf16`]
- [`char::from_digit`]
- [`char::from_u32_unchecked`]
- [`char::from_u32`]
- [`slice::partition_point`]
- [`str::rsplit_once`]
- [`str::split_once`]

The following previously stable APIs are now `const`.

- [`char::len_utf8`]
- [`char::len_utf16`]
- [`char::to_ascii_uppercase`]
- [`char::to_ascii_lowercase`]
- [`char::eq_ignore_ascii_case`]
- [`u8::to_ascii_uppercase`]
- [`u8::to_ascii_lowercase`]
- [`u8::eq_ignore_ascii_case`]

Rustdoc
-------
- [Rustdoc lints are now treated as a tool lint, meaning that
  lints are now prefixed with `rustdoc::` (e.g.
  `#[warn(rustdoc::non_autolinks)]`).][80527] Using the old style
  is still allowed, and will become a warning in a future release.
- [Rustdoc now supports argument files.][82261]
- [Rustdoc now generates smart punctuation for documentation.][79423]
- [You can now use "task lists" in Rustdoc Markdown.][81766] E.g.
  ```markdown
  - [x] Complete
  - [ ] Todo
  ```

Misc
----
- [You can now pass multiple filters to tests.][81356] E.g.
  `cargo test -- foo bar` will run all tests that match `foo` and `bar`.
- [Rustup now distributes PDB symbols for the `std` library on Windows,
  allowing you to see `std` symbols when debugging.][82218]

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.

- [Check the result cache before the DepGraph when ensuring queries][81855]
- [Try fast_reject::simplify_type in coherence before doing full check][81744]
- [Only store a LocalDefId in some HIR nodes][81611]
- [Store HIR attributes in a side table][79519]

Compatibility Notes
-------------------
- [Cargo build scripts are now forbidden from setting
  `RUSTC_BOOTSTRAP`.][cargo/9181]
- [Removed support for the `x86_64-rumprun-netbsd` target.][82863]
- [Deprecated the `x86_64-sun-solaris` target in favor of
  `x86_64-pc-solaris`.][82216]
- [Rustdoc now only accepts `,`, ` `, and `\t` as delimiters for specifying
  languages in code blocks.][78429]
- [Rustc now catches more cases of `pub_use_of_private_extern_crate`][80763]
- [Changes in how proc macros handle whitespace may lead to panics
  when used with older `proc-macro-hack` versions. A `cargo update` should
  be sufficient to fix this in all cases.][84136]

[84136]: rust-lang/rust#84136
[80763]: rust-lang/rust#80763
[82166]: rust-lang/rust#82166
[82121]: rust-lang/rust#82121
[81879]: rust-lang/rust#81879
[82261]: rust-lang/rust#82261
[82218]: rust-lang/rust#82218
[82216]: rust-lang/rust#82216
[82202]: rust-lang/rust#82202
[81855]: rust-lang/rust#81855
[81766]: rust-lang/rust#81766
[81744]: rust-lang/rust#81744
[81611]: rust-lang/rust#81611
[81479]: rust-lang/rust#81479
[81451]: rust-lang/rust#81451
[81356]: rust-lang/rust#81356
[80962]: rust-lang/rust#80962
[80553]: rust-lang/rust#80553
[80527]: rust-lang/rust#80527
[79519]: rust-lang/rust#79519
[79423]: rust-lang/rust#79423
[79208]: rust-lang/rust#79208
[78429]: rust-lang/rust#78429
[82733]: rust-lang/rust#82733
[82863]: rust-lang/rust#82863
[cargo/9181]: rust-lang/cargo#9181
[`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
[`Peekable::next_if`]: https://doc.rust-lang.org/stable/std/iter/struct.Peekable.html#method.next_if
[`Peekable::next_if_eq`]: https://doc.rust-lang.org/stable/std/iter/struct.Peekable.html#method.next_if_eq
[`Arguments::as_str`]: https://doc.rust-lang.org/stable/std/fmt/struct.Arguments.html#method.as_str
[`str::split_once`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.split_once
[`str::rsplit_once`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.rsplit_once
[`slice::partition_point`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.partition_point
[`char::len_utf8`]: https://doc.rust-lang.org/stable/std/primitive.char.html#method.len_utf8
[`char::len_utf16`]: https://doc.rust-lang.org/stable/std/primitive.char.html#method.len_utf16
[`char::to_ascii_uppercase`]: https://doc.rust-lang.org/stable/std/primitive.char.html#method.to_ascii_uppercase
[`char::to_ascii_lowercase`]: https://doc.rust-lang.org/stable/std/primitive.char.html#method.to_ascii_lowercase
[`char::eq_ignore_ascii_case`]: https://doc.rust-lang.org/stable/std/primitive.char.html#method.eq_ignore_ascii_case
[`u8::to_ascii_uppercase`]: https://doc.rust-lang.org/stable/std/primitive.u8.html#method.to_ascii_uppercase
[`u8::to_ascii_lowercase`]: https://doc.rust-lang.org/stable/std/primitive.u8.html#method.to_ascii_lowercase
[`u8::eq_ignore_ascii_case`]: https://doc.rust-lang.org/stable/std/primitive.u8.html#method.eq_ignore_ascii_case