Linux: Properly detect __GLIBCXX__ in atomicops.h

base/atomicops.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // For atomic operations on reference counts, see atomic_refcount.h.
 // For atomic operations on sequence numbers, see atomic_sequence_num.h.
 
 // The routines exported by this module are subtle.  If you use them, even if
 // you get the code right, it will depend on careful reasoning about atomicity
 // and memory ordering; it will be less readable, and harder to maintain.  If
@@ skipping 10 matching lines @@
 // versions are provided when no barriers are needed:
 //   NoBarrier_Store()
 //   NoBarrier_Load()
 // Although there are currently no compiler enforcement, you are encouraged
 // to use these.
 //
 
 #ifndef BASE_ATOMICOPS_H_
 #define BASE_ATOMICOPS_H_
 
-#include <cassert>  // Small C++ header which defines implementation specific
-                    // macros used to identify the STL implementation.
 #include <stdint.h>
 
+// Small C++ header which defines implementation specific macros used to
+// identify the STL implementation.
+// - libc++: captures __config for _LIBCPP_VERSION
+// - libstdc++: captures bits/c++config.h for __GLIBCXX__
+#include <cstddef>
+
 #include "base/base_export.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN) && defined(ARCH_CPU_64_BITS)
 // windows.h #defines this (only on x64). This causes problems because the
 // public API also uses MemoryBarrier at the public name for this fence. So, on
 // X64, undef it, and call its documented
 // (http://msdn.microsoft.com/en-us/library/windows/desktop/ms684208.aspx)
 // implementation directly.
 #undef MemoryBarrier
@@ skipping 155 matching lines @@
 #  endif
 #endif   // Portable / non-portable includes.
 
 // On some platforms we need additional declarations to make
 // AtomicWord compatible with our other Atomic* types.
 #if defined(OS_MACOSX) || defined(OS_OPENBSD)
 #include "base/atomicops_internals_atomicword_compat.h"
 #endif
 
 #endif  // BASE_ATOMICOPS_H_