Stabilize __jcvt

[folkertdev]

implementation: #1938
tracking issue: rust-lang/rust#147555

I think we should stabilize this intrinsic. The jsconv feature itself has been stable since 1.60.0. The intrinsic works as expected in ruffle, see ruffle-rs/ruffle#22138 (comment).

API surface

The stdarch_aarch64_jscvt feature contains one function:

Floating-point JavaScript convert to signed fixed-point, rounding toward zero

#[target_feature(enable = "jsconv")]
pub fn __jcvt(a: f64) -> i32;

[rustbot]

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[folkertdev]

@adamgemmell (or someone else from arm), could you give the changes to intrinsics_data/arm_intrinsics.json from #1938 a once-over just to make sure that is all correct?

[adamgemmell]

The JSON looks good to me. This intrinsic isn't part of Neon but it's fine for the JSON to say that to avoid having to edit some of stdarch's tests.

As was pointed out on the original rust PR the link to our documentation 404s, but I'll see if we can get this added to that page.

[traviscross]

@rfcbot fcp merge lang

(Doing the lang-side of the FCP from rust-lang/rust#147555; will check the lang boxes already checked there.)

[rust-rfcbot]

Team member @traviscross has proposed to merge this. The next step is review by the rest of the tagged team members:

• @joshtriplett
• @nikomatsakis
• @scottmcm
• @tmandry
• @traviscross

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

[rust-rfcbot]

🔔 This is now entering its final comment period, as per the review above. 🔔

[traviscross]

cc @RalfJung

[nikomatsakis]

@rfcbot reviewed