Add socketpair shim

Fixes rust-lang#3442
Design proposal: https://hackmd.io/`@tiif/Skhc1t0-C`

Rustup

Automatic Rustup

Minor fix: Change wording of epoll_create1 and socketpair's throw_unsup_format

This PR slightly changes the wording and format of ``epoll_create1``'s ``throw_unsup_format`` to match other shims. It is just a minor detail that I couldn't help but want to change while reading it. Sorry if it is not appropriate to open a PR for such minor detail.

… many times with different seeds

Implement LLVM x86 SSE4.2 intrinsics

SSE4.2 is arguably the least important SIMD extension for the x86 ISA, but it should still be supported for the sake of completeness.

…o three places

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Signed-off-by: onur-ozkan <work@onurozkan.dev>

And fix diagnostics for `self` from a macro.

cargo miri: add support for '--many-seeds'

to run the program / tests many times with different seeds: `cargo miri run --many-seeds` / `cargo miri test --many-seeds`.

`@rust-lang/miri` any opinion on the flag name here? Should it be `-Zmiri-many-seeds` or is `--many-seeds` fine?

Fixes rust-lang/miri#3546

Use `Variance` glob imported variants everywhere

Fully commit to using the globbed variance. Could be convinced the other way, and change this PR to not use the globbed variants anywhere, but I'd rather we do one or the other.

r? lcnr

…never-obligation, r=WaffleLapkin

Point out failing never obligation for `DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK`

Based on top of rust-lang#125289, so just need to look at the last commit.

r? `@WaffleLapkin`

MIR Shl/Shr: the offset can be computed with rem_euclid

r? ````@scottmcm````

…rors

Use a consistent way to filter out bounds instead of splitting it into three places

just a small cleanup, no logic change.

Initially the code had me looking for why anything was special here, only to realize there's nothing interesting going on

…=Kobzol

build `libcxx-version` only when it doesn't exist

In rust-lang#126423, it seems like c++ parsing takes quite amount of time on bootstrap startups. This PR makes libcxx-version to be compiled only when it doesn't exist.

A simple demonstration on the overhead of buiding `libcxx-version`:

```sh
$ rm -rf build/host/libcxx-version

$ x build
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.07s

 ----- LIBCXX VERSION CHECK TOOK: 509ms
Building tool rustdoc (stage1 -> stage2, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized] target(s) in 0.25s
Build completed successfully in 0:00:02

$ x build
Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.07s

 ----- LIBCXX VERSION CHECK TOOK: 2ms
Creating a sysroot for stage2 compiler (use `rustup toolchain link 'name' build/host/stage2`)
Building tool rustdoc (stage1 -> stage2, x86_64-unknown-linux-gnu)
    Finished `release` profile [optimized] target(s) in 0.14s
Build completed successfully in 0:00:01
```

…rrors

delegation: Fix hygiene for `self`

And fix diagnostics for `self` from a macro.

The missing rib caused `self` to be treated as a generic parameter and ignore `macro_rules` hygiene.

Addresses this comment rust-lang#124135 (comment).

…crum

make bors ignore comments in PR template

As discussed [here](https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/default.20PR.20description.20feedback/near/444794577), the existing PR template is not yet ignored by bors and the html comments show up in git history.

This PR uses markers so the html comments are deleted by the bot.

r? lcnr

…oing-things-once, r=jhpratt

std: suggest OnceLock over Once

It was noted in rust-lang#125615 (comment) that Once is not necessary in most cases and should be discouraged. Once is really just an implementation detail of OnceLock that others can use if they want. Suggest they use OnceLock instead.

Miri subtree update

r? `@ghost`