Tracking Issue for Hexagon arch intrinsics

Feature gate: #![feature(stdarch_hexagon)]

This is a tracking issue for the hexagon intrinsics in core::arch::hexagon.

Public API

Contents of core::arch::hexagon.

Steps

• Add HVX support to portable-simd (see https://github.com/rust-lang/portable-simd/pull/509)
• Let rustc emit the target features corresponding to each HVX rev (+hvxv65, +hvxv73, etc. -- see https://github.com/rust-lang/rust/pull/151500)
• Create target-specific mappings for the HVX intrinsics (see https://github.com/rust-lang/stdarch/pull/1999)
• Update the HVX intrinsics to be original "Q6" case https://github.com/rust-lang/stdarch/pull/2074
• Implement the RFC (cc @rust-lang/libs-team...
• Adjust documentation (see instructions on rustc-dev-guide)
• Style updates for any new syntax (nightly-style-procedure)
  • Style team decision on new formatting
  • Formatting for new syntax has been added to the Style Guide
  • (non-blocking) Formatting has been implemented in rustfmt
• Stabilization PR (see instructions on rustc-dev-guide)
• Fix for UNREACHABLE in llvm backend https://github.com/llvm/llvm-project/issues/182520
• Add scalar intrinsics https://github.com/rust-lang/stdarch/pull/2072

Start with the feature gate #![feature(stdarch_hexagon)] and the contents of core::arch::hexagon. Review the remaining checklist, especially the RFC, documentation and stabilization guidance, style requirements, and scalar intrinsics work. Done means the outstanding implementation, documentation, style, scalar-intrinsics, and stabilization steps are completed.