MIPS64: Fix NoBarrierAtomicValue.Construction test failure on big-endian

test/unittests/base/atomic-utils-unittest.cc

 // Copyright 2014 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.
 
 #include <limits.h>
 
 #include "src/base/atomic-utils.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace v8 {
@@ skipping 66 matching lines @@
 TEST(AtomicNumber, OperatorSubtractionAssignment) {
   AtomicNumber<size_t> a(std::numeric_limits<size_t>::max());
   AtomicNumber<size_t> b(std::numeric_limits<size_t>::max());
   a -= b.Value();
   EXPECT_EQ(a.Value(), 0u);
   EXPECT_EQ(b.Value(), std::numeric_limits<size_t>::max());
 }
 
 namespace {
 
-enum TestFlag {
+enum TestFlag : base::AtomicWord {
   kA,
   kB,
   kC,
 };
 
 }  // namespace
 
 
 TEST(AtomicValue, Initial) {
   AtomicValue<TestFlag> a(kA);
@@ skipping 167 matching lines @@
   a.Add(kAA);
   EXPECT_FALSE(a == b);
   EXPECT_TRUE(a != b);
   b.Add(kAA);
   EXPECT_TRUE(a == b);
   EXPECT_FALSE(a != b);
 }
 
 }  // namespace base
 }  // namespace v8