[NaCl SDK] Upate atomic ops in nacl_io

native_client_sdk/src/libraries/sdk_util/thread_pool.cc

Index: native_client_sdk/src/libraries/sdk_util/thread_pool.cc
diff --git a/native_client_sdk/src/libraries/sdk_util/thread_pool.cc b/native_client_sdk/src/libraries/sdk_util/thread_pool.cc
index e7d2e5cb6b295e6f8ce3fcc4599453073a41b898..1a2d2b8d29218a7006077cb053cf0402e271cba9 100644
--- a/native_client_sdk/src/libraries/sdk_util/thread_pool.cc
+++ b/native_client_sdk/src/libraries/sdk_util/thread_pool.cc
@@ -60,15 +60,7 @@ void ThreadPool::Setup(int counter, WorkFunction work, void *data) {
 // Return decremented task counter.  This function
 // can be called from multiple threads at any given time.
 int ThreadPool::DecCounter() {
-#if defined(__native_client__)
-  // Use fast atomic sub & fetch.
-  return __sync_sub_and_fetch(&counter_, 1);
-#else
-  // Fallback to a more platform independent pthread mutex via AutoLock.
-  static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
-  AutoLock lock(&mutex);
-  return --counter_;
-#endif
+  return AtomicAddFetch(&counter_, 1);
 }
 
 // Set exit flag, post and join all the threads in the pool.  This function is