Stabilize sha512. sm3 and sm4 for x86

[sayantn]

This PR stabilizes the feature flag sha512_sm_x86 (tracking issue #126624).

Public API

The 3 x86 target features sha512, sm3 and sm4, and the associated intrinsics in stdarch.

These target features are very specialized, and are only used to signal the presence of the corresponding CPU instruction. They don't have any nontrivial interaction with the ABI (contrary to something like AVX), and serve the only purpose of enabling 10 stdarch intrinsics, all of which have been implemented and propagated to rustc via a stdarch submodule update.

Associated PRs

• Added SHA512, SM3, SM4 target-features and sha512_sm_x86 feature gate #126704
• Add Runtime detection for SHA512, SM3 and SM4 stdarch#1592
• Implement SHA512, SM3 and SM4 intrinsics stdarch#1790
• Remove avx512dq and avx512vl implication for avx512fp16 #140389 (stdarch submodule update)

As all of the required tasks have been done (adding the target features to rustc, implementing their runtime detection in std_detect and implementing the associated intrinsics in core_arch), these target features can be stabilized now.

cc @rust-lang/lang
cc @rust-lang/libs-api for the intrinsics and runtime detection

@traviscross is this okay? Or do I have to give more details? (I don't think anyone else worked on this feature, so no one else to ping, maybe cc @Amanieu). I will send the reference pr soon

[rustbot]

⚠️ Warning ⚠️

• Some commits in this PR modify submodules.

[traviscross]

Stabilizing target features are somewhat minimal as far as stabilizations go, but still, this is going to need something more in the way of a stabilization report in the description of this PR. We need some narrative about what we're stabilizing here and a review of the evidence about why it's OK for us to stabilize this now. Have a look at our new template for this in rust-lang/rustc-dev-guide#2219.

Please think too about who else in the Project has worked on this or related things and who might therefore be interested in this, and please ping those people here.

This will also need a PR to the Reference documenting the change, and that should be linked from the stabilization report as well.

@rustbot labels +S-waiting-on-documentation

Please renominate when the stabilization report is available.

[traviscross]

Reminder to our future selves to be sure to pull out this "do not merge" commit

[sayantn]

This is to make the tests pass for now, once rust-lang/stdarch#1797 merges we can change it (so it has to merge before this, and so the libs-api fcp on #126624 has to merge)

[traviscross]

is this okay? Or do I have to give more details?

Thanks for adding the details above. @scottmcm, @RalfJung, @workingjubilee, anything more you want to see for this sort of thing?