[wasm][threads] Fix alignment of i64.atomic.wait

The alignment should be 3 (i.e. 8 bytes), but was specified as 2 (i.e. 4
bytes).

Bug: v8:9425
Change-Id: I0beb09df25fe0281ed604909e894afd804f5411e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1693836Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Ben Smith <binji@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62657}

src/wasm/function-body-decoder-impl.h

@@ -65,7 +65,7 @@ struct WasmException;
 #define ATOMIC_OP_LIST(V)                \
   V(AtomicNotify, Uint32)                \
   V(I32AtomicWait, Uint32)               \
-  V(I64AtomicWait, Uint32)               \
+  V(I64AtomicWait, Uint64)               \
   V(I32AtomicLoad, Uint32)               \
   V(I64AtomicLoad, Uint64)               \
   V(I32AtomicLoad8U, Uint8)              \

test/mjsunit/regress/wasm/regress-9425.js

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+// Flags: --experimental-wasm-threads
+
+load('test/mjsunit/wasm/wasm-module-builder.js');
+
+var builder = new WasmModuleBuilder();
+
+builder.addMemory(1, 1, /*exp*/ false, /*shared*/ true);
+
+builder.addFunction('test', kSig_v_v).addBody([
+  kExprI32Const, 0,                         //
+  kExprI64Const, 0,                         //
+  kExprI64Const, 0,                         //
+  kAtomicPrefix, kExprI64AtomicWait, 3, 0,  //
+  kExprDrop,                                //
+]);
+
+builder.instantiate();