Rollup merge of #147521 - sayantn:simd-const-intrinsics, r=madsmtm

Make SIMD intrinsics available in `const`-contexts

successor to rust-lang/rust#146568, this PR actually makes the SIMD intrinsics `const`, and modifies the tests to test the const-eval implementations

r? `@tgross35` ig (although feel free to reassign, this is not anything targeted really)

Author: matthiaskrgr

tests/pass/intrinsics/portable-simd.rs

@@ -60,7 +60,7 @@ impl<T: Copy, const N: usize> PackedSimd<T, N> {
 
 #[rustc_intrinsic]
 #[rustc_nounwind]
-pub unsafe fn simd_shuffle_const_generic<T, U, const IDX: &'static [u32]>(x: T, y: T) -> U;
+pub const unsafe fn simd_shuffle_const_generic<T, U, const IDX: &'static [u32]>(x: T, y: T) -> U;
 
 fn simd_ops_f16() {
     use intrinsics::*;