Insta-stabilize the methods `is_ready` and `is_pending` of `Poll`.

Possible because of the recent stabilization of const control flow.

Also adds a test for these methods in a const context.

Part of rust-lang#76268

POSIX leaves it implementation-defined whether `link` follows symlinks.
In practice, for example, on Linux it does not and on FreeBSD it does.
So, switch to `linkat`, so that we can pick a behavior rather than
depending on OS defaults.

Pick the option to not follow symlinks. This is somewhat arbitrary, but
seems the less surprising choice because hard linking is a very
low-level feature which requires the source and destination to be on
the same mounted filesystem, and following a symbolic link could end
up in a different mounted filesystem.

Due to the recent release of 1.47.0, this PR will be stabilized in 1.49.0 instead of 1.48.0.

Also mention that where possible, `hard_link` does not follow symlinks.

According to [the bionic status page], `linkat` has only been available
since API level 21. Since Android is based on Linux and Linux's `link`
doesn't follow symlinks, just use `link` on Android.

[the bionic status page]: https://android.googlesource.com/platform/bionic/+/master/docs/status.md

This adds a binary called `x` in `src/tools/x`. All it does is check the
current directory and its ancestors for a file called `x.py`, and if it
finds one, runs it.

By installing x, you can easily `x.py` from any subdirectory.

It can be installed globally with `cargo install --path src/tools/x`

Also includes:
- Cell::into_inner
- RefCell::into_inner
- Atomic*::into_inner

Previously, trying to allow this would give another error!

```
warning: unknown lint: `private_intra_doc_links`
 --> private.rs:1:10
  |
1 | #![allow(private_intra_doc_links)]
  |          ^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean: `broken_intra_doc_links`
  |
  = note: `#[warn(unknown_lints)]` on by default

warning: public documentation for `DocMe` links to private item `DontDocMe`
 --> private.rs:2:11
  |
2 | /// docs [DontDocMe]
  |           ^^^^^^^^^ this item is private
  |
  = note: `#[warn(private_intra_doc_links)]` on by default
  = note: this link will resolve properly if you pass `--document-private-items`
```

This is really starting to get out of hand. Rustdoc should instead allow
all lints in the rustdoc lint group.

Partially fix rust-lang#55002, deprecate in another release

Co-authored-by: Ashley Mannix <kodraus@hey.com>

Update stable version for stabilize_spin_loop

Co-authored-by: Joshua Nelson <joshua@yottadb.com>

Use better example for spinlock

As suggested by KodrAus

Remove renamed_spin_loop already available in master

Fix spin loop example

Includes:
- io::Cursor::new
- io::Cursor::get_ref
- io::Cursor::position
- io::empty
- io::repeat
- io::sink

…rAus

Stabilize hint::spin_loop

Partially fix rust-lang#55002, deprecate in another release

r? ```@KodrAus```

Stabilize `Poll::is_ready` and `is_pending` as const

Insta-stabilize the methods `is_ready` and `is_pending` of `std::task::Poll` as const, in the same way as [PR#76198](rust-lang#76198).

Possible because of the recent stabilization of const control flow.

Part of rust-lang#76225.

…olnay

Define `fs::hard_link` to not follow symlinks.

POSIX leaves it [implementation-defined] whether `link` follows symlinks.
In practice, for example, on Linux it does not and on FreeBSD it does.
So, switch to `linkat`, so that we can pick a behavior rather than
depending on OS defaults.

Pick the option to not follow symlinks. This is somewhat arbitrary, but
seems the less surprising choice because hard linking is a very
low-level feature which requires the source and destination to be on
the same mounted filesystem, and following a symbolic link could end
up in a different mounted filesystem.

[implementation-defined]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/link.html

make concurrency helper more pleasant to read

Recognize `private_intra_doc_links` as a lint

Previously, trying to allow this would give another error!

```
warning: unknown lint: `private_intra_doc_links`
 --> private.rs:1:10
  |
1 | #![allow(private_intra_doc_links)]
  |          ^^^^^^^^^^^^^^^^^^^^^^^ help: did you mean: `broken_intra_doc_links`
  |
  = note: `#[warn(unknown_lints)]` on by default

warning: public documentation for `DocMe` links to private item `DontDocMe`
 --> private.rs:2:11
  |
2 | /// docs [DontDocMe]
  |           ^^^^^^^^^ this item is private
  |
  = note: `#[warn(private_intra_doc_links)]` on by default
  = note: this link will resolve properly if you pass `--document-private-items`
```

Fixes the issue found in rust-lang#77249 (comment).

r? ````@Manishearth````

Does anyone know why this additional step is necessary? It seems weird this has to be declared in 3 different places.

… r=Mark-Simulacrum

BTreeMap: stop mistaking node for an orderly place

A second mistake in rust-lang#77612 was to ignore the node module's rightful comment "this module doesn't care whether the entries are sorted". And there's a much simpler way to visit the keys in order, if you check this separately from a single pass checking everything.

r? ````@Mark-Simulacrum````

…crum

fix some incorrect aliasing in the BTree

This line is wrong:
```
ptr::copy(slice.as_ptr().add(idx), slice.as_mut_ptr().add(idx + 1), slice.len() - idx);
```
When `slice.as_mut_ptr()` is called, that creates a mutable reference to the entire slice, which invalidates the raw pointer previously returned by `slice.as_ptr()`. (Miri currently misses this because raw pointers are not tracked properly.)

Cc ````@ssomers````

…-size, r=jyn514

Remove FIXME comment in print_type_sizes ui test suite

## Overview
Helps with rust-lang#62277

> The type sizes are likely only printed when the actual layout is computed. For generic types, this only happens during codegen.

ref: https://rust-lang.zulipchat.com/#narrow/stream/182449-t-compiler.2Fhelp/topic/Codegen.20process.20question/near/215836807

Some tests like `multiple_types.rs` are passed even if using `check-pass`. But tests should be agnostic to when the actual layout is computed. The `build-pass` is intentionally used for them. I remove FIXME comments.

Use SOCK_CLOEXEC and accept4() on more platforms.

This PR enables the use of `SOCK_CLOEXEC` and `accept4` on more platforms.

-----

Android uses the linux kernel, so it should also support it.

DragonflyBSD introduced them in 4.4 (December 2015):
https://www.dragonflybsd.org/release44/

FreeBSD introduced them in 10.0 (January 2014):
https://wiki.freebsd.org/AtomicCloseOnExec

Illumos introduced them in a commit in April 2013, not sure when it was released. It is quite possible that is has always been in Illumos:
illumos/illumos-gate@5dbfd19
https://illumos.org/man/3socket/socket
https://illumos.org/man/3socket/accept4

NetBSD introduced them in 6.0 (Oktober 2012) and 8.0 (July 2018):
https://man.netbsd.org/NetBSD-6.0/socket.2
https://man.netbsd.org/NetBSD-8.0/accept.2

OpenBSD introduced them in 5.7 (May 2015):
https://man.openbsd.org/socket https://man.openbsd.org/accept

Add a tool to run `x.py` from any subdirectory

This adds a binary called `x` in `src/tools/x`. All it does is check the current directory and its ancestors for a file called `x.py`, and if it finds one, runs it.

By installing x, you can easily run `x.py` from any subdirectory, and only need to type `x`.

It can be installed with `cargo install --path src/tools/x`

This is a copy of a [binary I've been using myself when working on rust](https://github.com/casey/bootstrap), currently published to crates.io as `bootstrap`.

It could be changed to avoid indirecting through `x.py`, and instead call the bootstrap module directly. However, this seemed like the simplest thing possible, and won't break if the details of how the bootstrap module is invoked change.

…=Mark-Simulacrum

Fix run-make tests running when LLVM is disabled

The `--cc`, `--cxx`, `--cflags` and `--ar` flags were only passed to compiletest when `builder.config.llvm_enabled()` returned true. This is preventing me from running the tests on cg_clif.

…lnay

Constantify `UnsafeCell::into_inner` and related

Tracking issue: rust-lang#78729

This PR constantifies:
- `UnsafeCell::into_inner`
- `Cell::into_inner`
- `RefCell::into_inner`
- `Atomic*::into_inner`

r? ```@dtolnay```

Correct unsigned equivalent of isize to be usize

See [rust-lang#74913 (comment)](rust-lang#74913 (comment)) for why this matters. Apparently it hasn't been used anywhere else, though CI will tell for sure.

Make some std::io functions `const`

Tracking issue: rust-lang#78812

Make the following functions `const`:
- `io::Cursor::new`
- `io::Cursor::get_ref`
- `io::Cursor::position`
- `io::empty`
- `io::repeat`
- `io::sink`

r? ```@dtolnay```

use single char patterns for split() (clippy::single_char_pattern)

…lcnr

Small cleanup in `TypeFoldable` derive macro

r? `@lcnr`