Initial SIMDBC interpreter.

runtime/vm/atomic_macos.h

Index: runtime/vm/atomic_macos.h
diff --git a/runtime/vm/atomic_macos.h b/runtime/vm/atomic_macos.h
index fd5af872c3f58e438424af42e4c78a70ddee7a8e..cd666d5d6fd83e4fe280efd1fc0141e2a5573ef1 100644
--- a/runtime/vm/atomic_macos.h
+++ b/runtime/vm/atomic_macos.h
@@ -36,7 +36,7 @@ inline void AtomicOperations::DecrementBy(intptr_t* p, intptr_t value) {
 }
 
 
-#if !defined(USING_SIMULATOR)
+#if !defined(USING_SIMULATOR_ATOMICS)
 inline uword AtomicOperations::CompareAndSwapWord(uword* ptr,
                                                   uword old_value,
                                                   uword new_value) {
@@ -49,7 +49,7 @@ inline uint32_t AtomicOperations::CompareAndSwapUint32(uint32_t* ptr,
                                                        uint32_t new_value) {
   return __sync_val_compare_and_swap(ptr, old_value, new_value);
 }
-#endif  // !defined(USING_SIMULATOR)
+#endif  // !defined(USING_SIMULATOR_ATOMICS)
 
 }  // namespace dart