Stabilize the avx512 target features

[sayantn]

This PR stabilizes the AVX512 target features - see this comment.

Tracking Issue - #44839

DO NOT MERGE now, because the runtime detection for 5 features are guarded on avx512_target_feature, so rust-lang/stdarch#1757 has a temporary fix which changes the feature name of these. We need to FCP these together with all the AVX512 target features, after that and merge of rust-lang/stdarch#1760, we can again do a stdarch update and merge this.

The target feature UI tests have been changed to cmpxchg16b (arbitrarily chosen, please comment if some other feature will be better)

Updates stdarch

Needs to wait for some stdarch fixes

[rustbot]

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[rustbot]

⚠️ Warning ⚠️

• These commits modify submodules.

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

[Amanieu]

Nominating for T-lang FCP. This stabilizes the AVX512 target features which is a per-requisite for stabilizing the AVX-512 intrinsics tracked in #111137.

[ehuss]

Can you also send a PR to update https://github.com/rust-lang/reference/blob/master/src/attributes/codegen.md#x86-or-x86_64?

[Amanieu]

These features are for the various AVX512 sub-features. We have already stabilized some of these names in is_x86_feature_detected! so the language level name should match.

[rustbot]

⚠️ Warning ⚠️

• Some commits in this PR modify submodules.

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] build_script_build test:false 0.571
error: unresolved link to `mem::MaybeUninit`
   --> library/core/src/../../stdarch/crates/core_arch/src/x86/avx512fp16.rs:267:55
    |
267 | /// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
    |                                                       ^^^^^^^^^^^^^^^^ no item named `mem` in scope
    |
    = note: `-D rustdoc::broken-intra-doc-links` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(rustdoc::broken_intra_doc_links)]`

error: unresolved link to `mem::zeroed`
   --> library/core/src/../../stdarch/crates/core_arch/src/x86/avx512fp16.rs:268:52
    |
268 | /// In practice, this is typically equivalent to [`mem::zeroed`].
    |                                                    ^^^^^^^^^^^ no item named `mem` in scope

error: unresolved link to `mem::MaybeUninit`
   --> library/core/src/../../stdarch/crates/core_arch/src/x86/avx512fp16.rs:280:55
    |
280 | /// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
    |                                                       ^^^^^^^^^^^^^^^^ no item named `mem` in scope

error: unresolved link to `mem::zeroed`
   --> library/core/src/../../stdarch/crates/core_arch/src/x86/avx512fp16.rs:281:52
    |
281 | /// In practice, this is typically equivalent to [`mem::zeroed`].
    |                                                    ^^^^^^^^^^^ no item named `mem` in scope

error: unresolved link to `mem::MaybeUninit`
   --> library/core/src/../../stdarch/crates/core_arch/src/x86/avx512fp16.rs:293:55
    |
293 | /// picks some valid value and is not equivalent to [`mem::MaybeUninit`].
    |                                                       ^^^^^^^^^^^^^^^^ no item named `mem` in scope

error: unresolved link to `mem::zeroed`
   --> library/core/src/../../stdarch/crates/core_arch/src/x86/avx512fp16.rs:294:52
    |
294 | /// In practice, this is typically equivalent to [`mem::zeroed`].
    |                                                    ^^^^^^^^^^^ no item named `mem` in scope

error: could not document `core`
warning: build failed, waiting for other jobs to finish...
[RUSTC-TIMING] core test:false 12.870
Command has failed. Rerun with -v to see more details.
Build completed unsuccessfully in 0:00:13
  local time: Thu Apr 10 10:31:34 UTC 2025
  network time: Thu, 10 Apr 2025 10:31:35 GMT
##[error]Process completed with exit code 1.
Post job cleanup.