Make NoReloadScope thread safe

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 479ca30b35394bc25c799efacbf1293377297839..cdd57d4df658382df0ec27c67bf51118d737802c 100644
--- a/runtime/vm/atomic_macos.h
+++ b/runtime/vm/atomic_macos.h
@@ -21,6 +21,11 @@ inline uintptr_t AtomicOperations::FetchAndIncrement(uintptr_t* p) {
 }
 
 
+inline intptr_t AtomicOperations::FetchAndIncrement(intptr_t* p) {
+  return __sync_fetch_and_add(p, 1);
+}
+
+
 inline void AtomicOperations::IncrementBy(intptr_t* p, intptr_t value) {
   __sync_fetch_and_add(p, value);
 }
@@ -36,6 +41,11 @@ inline uintptr_t AtomicOperations::FetchAndDecrement(uintptr_t* p) {
 }
 
 
+inline intptr_t AtomicOperations::FetchAndDecrement(intptr_t* p) {
+  return __sync_fetch_and_sub(p, 1);
+}
+
+
 inline void AtomicOperations::DecrementBy(intptr_t* p, intptr_t value) {
   __sync_fetch_and_sub(p, value);
 }