Stabilize Wasm relaxed SIMD

Author: daxpedda

compiler/rustc_target/src/target_features.rs

@@ -330,7 +330,7 @@ const WASM_ALLOWED_FEATURES: &[(&str, Stability)] = &[
     ("mutable-globals", Stable),
     ("nontrapping-fptoint", Stable),
     ("reference-types", Unstable(sym::wasm_target_feature)),
-    ("relaxed-simd", Unstable(sym::wasm_target_feature)),
+    ("relaxed-simd", Stable),
     ("sign-ext", Stable),
     ("simd128", Stable),
     // tidy-alphabetical-end

library/stdarch

@@ -0,0 +1,9 @@
+//@ only-wasm32-wasip1
+//@ compile-flags: -Ctarget-feature=+relaxed-simd,+simd128 --crate-type=lib
+//@ build-pass
+
+use std::arch::wasm32::*;
+
+pub fn test(a: v128, b: v128, m: v128) -> v128 {
+    i64x2_relaxed_laneselect(a, b, m)
+}