Switch NaCl code to use GCC intrinsics for atomic ops.

src/include/nacl/atomic_ops.h

-/*
- * Copyright (c) 2011 The Native Client Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-#ifndef NATIVE_CLIENT_SRC_INCLUDE_NACL_ATOMIC_OPS_H_
-#define NATIVE_CLIENT_SRC_INCLUDE_NACL_ATOMIC_OPS_H_ 1
-
-#include "native_client/src/include/portability.h"
-#include <stdint.h>
-
-typedef int32_t Atomic32;
-
-static INLINE Atomic32 CompareAndSwap(volatile Atomic32* ptr,
-                                      Atomic32 old_value,
-                                      Atomic32 new_value) {
-  return __sync_val_compare_and_swap(ptr, old_value, new_value);
-}
-
-static INLINE Atomic32 AtomicExchange(volatile Atomic32* ptr,
-                                      Atomic32 new_value) {
-  return __sync_lock_test_and_set(ptr, new_value);
-}
-
-static INLINE Atomic32 AtomicIncrement(volatile Atomic32* ptr,
-                                       Atomic32 increment) {
-  return __sync_add_and_fetch(ptr, increment);
-}
-
-#endif  /* NATIVE_CLIENT_SRC_INCLUDE_NACL_ATOMIC_OPS_H_ */