Improve the performance of bit set searches with a compiler intrinsic.

runtime/platform/utils_macos.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-#ifndef VM_CPU_H_
-#define VM_CPU_H_
-
-#include "vm/allocation.h"
+#ifndef PLATFORM_UTILS_MACOS_H_
+#define PLATFORM_UTILS_MACOS_H_
 
 namespace dart {
 
-// Forward Declarations.
-class Error;
-class Instance;
+inline int Utils::CountTrailingZeros(uint32_t x) {
+  return __builtin_ctzl(x);
+};
 
-
-class CPU : public AllStatic {
- public:
-  static void FlushICache(uword start, uword size);
-  static const char* Id();
+inline int Utils::CountTrailingZeros(uint64_t x) {
+  return __builtin_ctzll(x);
 };
 
 }  // namespace dart
 
-#endif  // VM_CPU_H_
+#endif  // PLATFORM_UTILS_MACOS_H_