curve25519-dalek using unstable features

[flihp]

Nightly 1.78 has started complaining about curve25519-dalek using unstable features:

error[E0658]: use of unstable library feature 'stdarch_x86_avx512'
  --> /home/flihp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.1/src/backend/vector/ifma/field.rs:26:5
   |
26 |     _mm256_madd52lo_epu64(z.into(), x.into(), y.into()).into()
   |     ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #111137 <https://github.com/rust-lang/rust/issues/111137> for more information
   = help: add `#![feature(stdarch_x86_avx512)]` to the crate attributes to enable
   = note: this compiler was built on 2024-02-07; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature 'stdarch_x86_avx512'
  --> /home/flihp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.1/src/backend/vector/ifma/field.rs:25:9
   |
25 |     use core::arch::x86_64::_mm256_madd52lo_epu64;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #111137 <https://github.com/rust-lang/rust/issues/111137> for more information
   = help: add `#![feature(stdarch_x86_avx512)]` to the crate attributes to enable
   = note: this compiler was built on 2024-02-07; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature 'stdarch_x86_avx512'
  --> /home/flihp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.1/src/backend/vector/ifma/field.rs:34:5
   |
34 |     _mm256_madd52hi_epu64(z.into(), x.into(), y.into()).into()
   |     ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #111137 <https://github.com/rust-lang/rust/issues/111137> for more information
   = help: add `#![feature(stdarch_x86_avx512)]` to the crate attributes to enable
   = note: this compiler was built on 2024-02-07; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature 'stdarch_x86_avx512'
  --> /home/flihp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.1/src/backend/vector/ifma/field.rs:33:9
   |
33 |     use core::arch::x86_64::_mm256_madd52hi_epu64;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #111137 <https://github.com/rust-lang/rust/issues/111137> for more information
   = help: add `#![feature(stdarch_x86_avx512)]` to the crate attributes to enable
   = note: this compiler was built on 2024-02-07; consider upgrading it if it is out of date

It's also noting use of an unknown feature:

error[E0635]: unknown feature `stdsimd`
  --> /home/flihp/.cargo/registry/src/index.crates.io-6f17d22bba15001f/curve25519-dalek-4.1.1/src/lib.rs:13:70
   |
13 | #![cfg_attr(all(curve25519_dalek_backend = "simd", nightly), feature(stdsimd))]
   |                                                                      ^^^^^^^

1.76 had nothing to say about the same code

[flihp]

see:

• Build fails on nightly-2024-02-05 dalek-cryptography/curve25519-dalek#618
• Fix nightly build dalek-cryptography/curve25519-dalek#619
• curve,ed,x: Bump patch version to reflect fix to nightly SIMD build dalek-cryptography/curve25519-dalek#621
• Crate fails with nightly-2024-02-06 dalek-cryptography/curve25519-dalek#622

[flihp]

recommended fix seems to be: nightly compilers after nightly-2024-02-04 require curve25519-dalek > v4.1.1 ... turning this into an "upgrade curve25519-dalek to 4.1.2" issue