Squashed 'third_party/boostorg/atomic/' content from commit 19eecf8

Change-Id: I4723a39ab79969b4c0d7b7e67a4143c4e02992ed
git-subtree-dir: third_party/boostorg/atomic
git-subtree-split: 19eecf893c665410de63ab6ebb8549f405703e80
diff --git a/include/boost/atomic/atomic_flag.hpp b/include/boost/atomic/atomic_flag.hpp
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+++ b/include/boost/atomic/atomic_flag.hpp
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+/*
+ * Distributed under the Boost Software License, Version 1.0.
+ * (See accompanying file LICENSE_1_0.txt or copy at
+ * http://www.boost.org/LICENSE_1_0.txt)
+ *
+ * Copyright (c) 2011 Helge Bahmann
+ * Copyright (c) 2013 Tim Blechmann
+ * Copyright (c) 2014 Andrey Semashev
+ */
+/*!
+ * \file   atomic/atomic_flag.hpp
+ *
+ * This header contains definition of \c atomic_flag.
+ */
+
+#ifndef BOOST_ATOMIC_ATOMIC_FLAG_HPP_INCLUDED_
+#define BOOST_ATOMIC_ATOMIC_FLAG_HPP_INCLUDED_
+
+#include <boost/atomic/capabilities.hpp>
+#include <boost/atomic/detail/operations.hpp>
+#include <boost/atomic/detail/atomic_flag.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+
+using atomics::atomic_flag;
+
+} // namespace boost
+
+#endif // BOOST_ATOMIC_ATOMIC_FLAG_HPP_INCLUDED_