Bug 1725797 - Fix + use wasmRelaxedSimdEnabled. r=rhunt

The WasmFeature for relaxed SIMD was spec'd too weakly: in
moz.configure, relaxed SIMD depends on normal SIMD, but the
WasmFeature did not have the proper dependency.  So add that.

Now that wasmRelaxedSimdEnabled() implies wasmSimdEnabled(), we can
use the former predicate alone to guard relaxed-SIMD tests.

Differential Revision: https://phabricator.services.mozilla.com/D122668

js/public/WasmFeatures.h

@@ -132,8 +132,7 @@
                /* lower case name    */ v128Relaxed,                          \
                /* compile predicate  */ WASM_RELAXED_SIMD_ENABLED,            \
                /* compiler predicate */ AnyCompilerAvailable(cx),             \
-               /* flag predicate     */ !IsFuzzingCranelift(cx) &&            \
-               js::jit::JitSupportsWasmSimd(),                                \
+               /* flag predicate     */ WasmSimdFlag(cx),                     \
                /* shell flag         */ "relaxed-simd",                       \
                /* preference name    */ "relaxed_simd")                       \
   EXPERIMENTAL(/* capitalized name   */ Memory64,                             \

js/src/jit-test/tests/wasm/simd/experimental.js

@@ -1,4 +1,4 @@
-// |jit-test| --wasm-relaxed-simd; skip-if: !wasmSimdEnabled()
+// |jit-test| --wasm-relaxed-simd; skip-if: !wasmRelaxedSimdEnabled()
 
 // Experimental opcodes.  We have no text parsing support for these yet.  The
 // tests will be cleaned up and moved into ad-hack.js if the opcodes are