Move atomic ops and related files to base library

src/once.cc

-// Copyright 2012 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "src/once.h"
-
-#ifdef _WIN32
-#include <windows.h>
-#else
-#include <sched.h>
-#endif
-
-#include "src/atomicops.h"
-
-namespace v8 {
-namespace internal {
-
-void CallOnceImpl(OnceType* once, PointerArgFunction init_func, void* arg) {
-  AtomicWord state = Acquire_Load(once);
-  // Fast path. The provided function was already executed.
-  if (state == ONCE_STATE_DONE) {
-    return;
-  }
-
-  // The function execution did not complete yet. The once object can be in one
-  // of the two following states:
-  //   - UNINITIALIZED: We are the first thread calling this function.
-  //   - EXECUTING_FUNCTION: Another thread is already executing the function.
-  //
-  // First, try to change the state from UNINITIALIZED to EXECUTING_FUNCTION
-  // atomically.
-  state = Acquire_CompareAndSwap(
-      once, ONCE_STATE_UNINITIALIZED, ONCE_STATE_EXECUTING_FUNCTION);
-  if (state == ONCE_STATE_UNINITIALIZED) {
-    // We are the first thread to call this function, so we have to call the
-    // function.
-    init_func(arg);
-    Release_Store(once, ONCE_STATE_DONE);
-  } else {
-    // Another thread has already started executing the function. We need to
-    // wait until it completes the initialization.
-    while (state == ONCE_STATE_EXECUTING_FUNCTION) {
-#ifdef _WIN32
-      ::Sleep(0);
-#else
-      sched_yield();
-#endif
-      state = Acquire_Load(once);
-    }
-  }
-}
-
-} }  // namespace v8::internal