Co-authored-by: Ralf Jung <post@ralfj.de>

General improvements, and also aims to better encourage the reader
to actually check out Arc::try_unwrap.

Currently, when building with `build-std`, some library build scripts
check properties of the target by inspecting the target triple at
`env::TARGET`, which is simply set to the filename of the JSON file
when using JSON target files.

This patch alters these build scripts to use `env::CARGO_CFG_*` to
fetch target information instead, allowing JSON target files
describing platforms without `restricted_std` to build correctly when
using `-Z build-std`.

Fixes wg-cargo-std-aware/rust-lang#60.

References refer to allocated objects

Partially addresses rust-lang/unsafe-code-guidelines#465

…trochenkov

Suppress unhelpful diagnostics for unresolved top level attributes

Fixes rust-lang#118455, unresolved top level attribute error didn't imported prelude and already have emitted an error, report builtin macro and attributes error by the way, so `check_invalid_crate_level_attr` in can ignore them.

Also fixes rust-lang#89566, fixes rust-lang#67107.

r? ``@petrochenkov``

Add support for custom JSON targets when using build-std.

Currently, when building with `build-std`, some library build scripts check properties of the target by inspecting the target triple at `env::TARGET`, which is simply set to the filename of the JSON file when using JSON target files.

This patch alters these build scripts to use `env::CARGO_CFG_*` to fetch target information instead, allowing JSON target files describing platforms without `restricted_std` to build correctly when using `-Z build-std`. There are some weak assertions here (for example, `nintendo && newlib`), however this seems at least a marginal improvement on the existing solution.

Fixes rust-lang/wg-cargo-std-aware#60.

…, r=Mark-Simulacrum

Always check the result of `pthread_mutex_lock`

Fixes rust-lang#120147.

Instead of manually adding a list of "good" platforms, I've simply made the check unconditional. pthread's mutex is already quite slow on most platforms, so one single well-predictable branch shouldn't hurt performance too much.

…ark-Simulacrum

Improve documentation for [A]Rc::into_inner

General improvements, and also aims to better encourage the reader to actually check out Arc::try_unwrap.

This addresses concerns from rust-lang#106894 (comment).

Rendered:

![Screenshot_20240123_114436](https://github.com/rust-lang/rust/assets/3986214/68896d62-13e0-4f3a-8073-91d8e77c5554)
![Screenshot_20240123_114455](https://github.com/rust-lang/rust/assets/3986214/dc58e4bd-dd7f-40b1-bc50-fd6200dde593)

…120040, r=ChrisDenton

Adjust Behaviour of `read_dir` and `ReadDir` in Windows Implementation: Check Whether Path to Search In Exists

This pull request changes the `read_dir` function's and the `ReadDir` structure's internal implementations for the Windows operating system to make its behaviour more accurate.

It should be noted that `ERROR_FILE_NOT_FOUND` is returned by the `FindFirstFileW` function when *no matching files can be found*, not necessarily that the path to search in does not exist in the first place. Therefore, directly returning the "The system cannot find the file specified." may not be accurate.

An extra check for whether the path to search in exists is added, returning a constructed `ReadDir` iterator with its handle being an `INVALID_HANDLE_VALUE` returned by the `FindFirstFileW` function if `ERROR_FILE_NOT_FOUND` is indeed the last OS error. The `ReadDir` implementation for the Windows operating system is correspondingly updated to always return `None` if the handle it has is an `INVALID_HANDLE_VALUE` which can only be the case if and only if specifically constructed by the `read_dir` function in the aforementioned conditions.

It should also be noted that `FindFirstFileW` would have returned `ERROR_PATH_NOT_FOUND` if the path to search in does not exist in the first place.

Presumably fixes rust-lang#120040.