Bump stdarch submodule and remove special handling for LLVM intrinsics that are no longer needed Bumps stdarch to pull https://github.com/rust-lang/stdarch/pull/1477, which reimplemented some functions with portable SIMD intrinsics instead of arch specific LLVM intrinsics. Handling of those LLVM intrinsics is removed from cranelift codegen and miri. cc `@RalfJung` `@bjorn3`