Require gcc >= 4.7 to use standard atomics.
diff --git a/asio/include/asio/detail/config.hpp b/asio/include/asio/detail/config.hpp
index b59286b..99a2e0a 100644
--- a/asio/include/asio/detail/config.hpp
+++ b/asio/include/asio/detail/config.hpp
@@ -309,11 +309,11 @@
# endif // (__cplusplus >= 201103)
# endif // defined(__clang__)
# if defined(__GNUC__)
-# if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ > 4)
+# if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4)
# if defined(__GXX_EXPERIMENTAL_CXX0X__)
# define ASIO_HAS_STD_ATOMIC 1
# endif // defined(__GXX_EXPERIMENTAL_CXX0X__)
-# endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 5)) || (__GNUC__ > 4)
+# endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4)
# endif // defined(__GNUC__)
# if defined(ASIO_MSVC)
# if (_MSC_VER >= 1700)