[wasm] Handle multi-value return in compiled fuzzing result

When a function returns multiple result, we check the only the first
result. We correctly get the first return value from the interpreter
results, but did not handle the compiled code correctly, which returns a
JSArray.

Bug: chromium:1153406
Change-Id: I32198cea131cab18094fac3e66a44e976907773d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2562816Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71488}

test/common/wasm/wasm-module-runner.cc

@@ -237,6 +237,13 @@ int32_t CallWasmFunctionForTesting(Isolate* isolate,
     return -1;
   }
   Handle<Object> result = retval.ToHandleChecked();
+
+  // Multi-value returns, get the first return value (see InterpretWasmModule).
+  if (result->IsJSArray()) {
+    auto receiver = Handle<JSReceiver>::cast(result);
+    result = JSObject::GetElement(isolate, receiver, 0).ToHandleChecked();
+  }
+
   if (result->IsSmi()) {
     return Smi::ToInt(*result);
   }