ARM64: Enable shorten-64-to-32 warning

src/arm64/utils-arm64.cc

 // Copyright 2013 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.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/utils-arm64.h"
 
 
 namespace v8 {
@@ skipping 56 matching lines @@
   // value =   h+g+f+e     d+c+b+a
   //                  \          |
   // value =       h+g+f+e+d+c+b+a
   value = ((value >> 1) & 0x5555555555555555) + (value & 0x5555555555555555);
   value = ((value >> 2) & 0x3333333333333333) + (value & 0x3333333333333333);
   value = ((value >> 4) & 0x0f0f0f0f0f0f0f0f) + (value & 0x0f0f0f0f0f0f0f0f);
   value = ((value >> 8) & 0x00ff00ff00ff00ff) + (value & 0x00ff00ff00ff00ff);
   value = ((value >> 16) & 0x0000ffff0000ffff) + (value & 0x0000ffff0000ffff);
   value = ((value >> 32) & 0x00000000ffffffff) + (value & 0x00000000ffffffff);
 
-  return value;
+  return static_cast<int>(value);
 }
 
 
 uint64_t LargestPowerOf2Divisor(uint64_t value) {
   return value & -value;
 }
 
 
 int MaskToBit(uint64_t mask) {
   DCHECK(CountSetBits(mask, 64) == 1);
   return CountTrailingZeros(mask, 64);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64