Stabilize most of `io_error_more`

Sadly, venting my frustration with t-libs-api is not a constructive way to solve problems and get things done, so I will try to stick to stuff that actually matters here.

- Tracking issue for this feature was opened 3 years ago: #86442
- FCP to stabilize it was completed 19(!!) months ago: rust-lang/rust#86442 (comment)
- A PR with stabilization was similarly open for 19 months: #106375, but nothing ever came out of it. Presumably (it is hard to judge given the lack of communication) because a few of the variants still had some concerns voiced about them, even after the FCP.

So, to highlight a common sentiment:

> Maybe uncontroversial variants can be stabilised first and other variants (such as `QuotaExceeded` or `FilesystemLoop`) later? [^1]

[^1]: rust-lang/rust#106375 (comment)

> I would like to voice support stabilization of the uncontroversial variants. This would get those variants to stable and focus the discussion around the more controversial ones. I don't see any particular reason that all of these must be stabilized at the same time. [...] [^2]

[^2]: rust-lang/rust#106375 (comment)

> Maybe some less-controversial subset could be stabilized sooner? What’s blocking this issue from making progress? [^3]

[^3]: rust-lang/rust#86442 (comment) (got 30 upvotes btw) (and no response)

So this is exactly what this PR does. It stabilizes the non-controversial variants now, leaving just a few of them behind.

Namely, this PR stabilizes:

- `HostUnreachable`
- `NetworkUnreachable`
- `NetworkDown`
- `NotADirectory`
- `IsADirectory`
- `DirectoryNotEmpty`
- `ReadOnlyFilesystem`
- `StaleNetworkFileHandle`
- `StorageFull`
- `NotSeekable`
- `FileTooLarge`
- `ResourceBusy`
- `ExecutableFileBusy`
- `Deadlock`
- `TooManyLinks`
- `ArgumentListTooLong`
- `Unsupported`

This PR does not stabilize:
- `FilesystemLoop`
- `FilesystemQuotaExceeded`
- `CrossesDevices`
- `InvalidFilename`

Hopefully, this will allow us to move forward with this highly and long awaited addition to std, both allowing to still polish the less clear parts of it and not leading to stagnation.

r? joshtriplett
because they seem to be listed as a part of t-libs-api and were one of the most responsive persons previously

use  `download-ci-llvm=true` in the default compiler config

rust-lang/rust@1ca2708 made it so that the `src/llvm-project` submodule has to be checkout for `download-ci-llvm = "if-unchanged"` to know if the submodule has been changed, but that is not required, if the submodule hasn't been checkout it cannot have been modified.

~~This PR restore the previous behavior by only updating the submodule if it has already been checkout.~~

This PR makes `download-ci-llvm = true` check if CI llvm is available and make it the default for the compiler profile, as to prevent unnecessarily checking out `src/llvm-project` with `"if-unchanged"`.

r? `````@onur-ozkan`````

Add test to build crates used by r-a on stable

r? ````````@Kobzol````````

I've opened other PRs for this one to work and they've landed already. I cherry-picked your commit, and added the last remaining pieces we needed I think.

…tmiasko

Remove `serialized_bitcode` from `LtoModuleCodegen`.

It's unused.

r? ``@bjorn3``

[illumos] enable SIGSEGV handler to detect stack overflows

Use the same code as Solaris. I couldn't find any tests regarding this, but I did test a stage0 build against my stack-exhaust-test binary [1]. Before:

```
running with use_stacker = No, new_thread = false, make_large_local = false
zsh: segmentation fault (core dumped)  cargo run
```

After:

```
running with use_stacker = No, new_thread = false, make_large_local = false

thread 'main' has overflowed its stack
fatal runtime error: stack overflow
zsh: IOT instruction (core dumped)  cargo +stage0 run
```

Fixes #128568.

[1] https://github.com/sunshowers/stack-exhaust-test/

bootstrap `naked_asm!` for `compiler-builtins`

tracking issue: rust-lang/rust#90957
parent PR: rust-lang/rust#128651

in this PR, `naked_asm!` is added as an alias for `asm!` with one difference: `options(noreturn)` is always enabled by `naked_asm!`. That makes it future-compatible for when `naked_asm!` starts disallowing `options(noreturn)` later.

The `naked_asm!` macro must be introduced first so that we can upgrade `compiler-builtins` to use it, and can then change the implementation of `naked_asm!` in rust-lang/rust#128651

I've added some usages for `naked_asm!` in the tests, so we can be confident that it works, but I've left upgrading the whole test suite to the parent PR.

r? ``@Amanieu``

Helper function for formatting with `LifetimeSuggestionPosition`

move some const fn out of the const_ptr_as_ref feature

When a `const fn` is still `#[unstable]`, it should generally use the same feature to track its regular stability and const-stability. Then when that feature moves towards stabilization we can decide whether the const-ness can be stabilized as well, or whether it should be moved into a new feature.

Also, functions like `ptr::as_ref` (which returns an `Option<&mut T>`) require `is_null`, which is tricky and blocked on some design concerns (see #74939). So move those to the is_null feature gate, as they should be stabilized together with `ptr.is_null()`.

Affects #91822, #122034, #75402, rust-lang/rust#74939

Rollup of 11 pull requests

Successful merges:

 - #128316 (Stabilize most of `io_error_more`)
 - #129473 (use  `download-ci-llvm=true` in the default compiler config)
 - #129529 (Add test to build crates used by r-a on stable)
 - #129981 (Remove `serialized_bitcode` from `LtoModuleCodegen`.)
 - #130094 (Inform the solver if evaluation is concurrent)
 - #130132 ([illumos] enable SIGSEGV handler to detect stack overflows)
 - #130146 (bootstrap `naked_asm!` for `compiler-builtins`)
 - #130149 (Helper function for formatting with `LifetimeSuggestionPosition`)
 - #130152 (adapt a test for llvm 20)
 - #130162 (bump download-ci-llvm-stamp)
 - #130164 (move some const fn out of the const_ptr_as_ref feature)

r? `@ghost`
`@rustbot` modify labels: rollup

rustdoc rfc#3662 changes under unstable flags

* All new functionality is under unstable options
* Adds `--merge=shared|none|finalize` flags
* Adds `--parts-out-dir=<crate specific directory>` for `--merge=none`
to write cross-crate info file for a single crate
* Adds `--include-parts-dir=<previously specified directory>` for
`--merge=finalize` to write cross-crate info files
* `tests/rustdoc/` tests for the new flags

Also emit `missing_docs` lint with `--test` to fulfil expectations

This PR removes the "test harness" suppression of the `missing_docs` lint to be able to fulfil `#[expect]` (expectations) as it is now "relevant".

I think the goal was to maybe avoid false-positive while linting on public items under `#[cfg(test)]` but with effective visibility we should no longer have any false-positive.

Another possibility would be to query the lint level and only emit the lint if it's of expect level, but that is even more hacky.

Fixes rust-lang/rust#130021

try-job: x86_64-gnu-aux

Ban non-array SIMD

Nearing the end of rust-lang/compiler-team#621 !

Currently blocked on ~~rust-lang/compiler-builtins#673 ~~rust-lang/compiler-builtins#674 ~~rust-lang/rust#129400 ~~rust-lang/rust#129481 for windows.

rustdoc: unify the short-circuit on all lints

This is a bit of an experiment to see if it improves perf.