Stabilize sha512. sm3 and sm4 for x86

[sayantn]

Stabilize the sha512, sm3 and sm4 target features for x86 (and their runtime detection and associated intrinsics in core_arch) (#126624)

@rustbot label O-x86_32 O-x86_64 A-target-feature I-lang-nominated T-lang -T-compiler -T-libs
r? lang

[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.