[vm] Implement more efficient CAS in simarm/simarm64 modes

runtime/vm/atomic.h

Index: runtime/vm/atomic.h
diff --git a/runtime/vm/atomic.h b/runtime/vm/atomic.h
index 41dfad18d4911376c83d602d268ffb523f364229..4a45506e443e82d84e5e52fed2e8e9f40de5524a 100644
--- a/runtime/vm/atomic.h
+++ b/runtime/vm/atomic.h
@@ -8,7 +8,6 @@
 #include "platform/globals.h"
 
 #include "vm/allocation.h"
-#include "vm/simulator.h"
 
 namespace dart {
 
@@ -62,16 +61,6 @@ class AtomicOperations : public AllStatic {
 
 }  // namespace dart
 
-#if defined(USING_SIMULATOR) && !defined(TARGET_ARCH_DBC)
-#define USING_SIMULATOR_ATOMICS
-#endif
-
-#if defined(USING_SIMULATOR_ATOMICS)
-// We need to use the simulator to ensure that atomic operations are observed
-// both in C++ and in generated code if the simulator is active.
-#include "vm/atomic_simulator.h"
-#endif
-
 #if defined(HOST_OS_ANDROID)
 #include "vm/atomic_android.h"
 #elif defined(HOST_OS_FUCHSIA)