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

runtime/platform/utils_macos.h

Index: runtime/platform/utils_macos.h
diff --git a/runtime/vm/cpu.h b/runtime/platform/utils_macos.h
similarity index 50%
copy from runtime/vm/cpu.h
copy to runtime/platform/utils_macos.h
index c8f5e9c034817c45c03482b163e1b9b93732b2e6..d0e068644eb226ab5be4ff150f11709682fa6c13 100644
--- a/runtime/vm/cpu.h
+++ b/runtime/platform/utils_macos.h
@@ -2,24 +2,19 @@
 // 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_