Stabilize __m512i, __m512, and __m512d

[scottmcm]

While there might be some uncertainty still with all the intrinsics and other related items, could we perhaps stabilize the types?

It seems like there's not much choice to be had, since m512 is definitely f32x16 and m512d is likewise f64x8.

I didn't include __m512bh since __m128bh is also unstable.

https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/Stabilizing.20AVX2.20.26.20AVX512.20*types*/near/362541037

[rustbot]

r? @Amanieu

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[Amanieu]

These types are independently useful even without the intrinsics since they can be used with inline assembly.

@rfcbot fcp merge

[rfcbot]

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

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se

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!

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[scottmcm]

FYI @dtolnay, it looks from the edit history like you attempted to check a box, but somehow rfcbot then removed your checkmark?

[rfcbot]

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

psst @Amanieu, I wasn't able to add the final-comment-period label, please do so.

[rfcbot]

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

psst @Amanieu, I wasn't able to add the finished-final-comment-period label, please do so.