Changed taking address of the values involved in bitwise_cast to avoi…

…d gcc warnings.

include/boost/atomic/detail/bitwise_cast.hpp

@@ -29,6 +29,17 @@ namespace boost {
 namespace atomics {
 namespace detail {
 
+template< typename T >
+BOOST_FORCEINLINE T* addressof(T& value) BOOST_NOEXCEPT
+{
+    // Note: The point of using a local struct as the intermediate type instead of char is to avoid gcc warnings
+    // if T is a const volatile char*:
+    // warning: casting ‘const volatile char* const’ to ‘const volatile char&’ does not dereference pointer
+    // The local struct makes sure T is not related to the cast target type.
+    struct opaque_type;
+    return reinterpret_cast< T* >(&const_cast< opaque_type& >(reinterpret_cast< const volatile opaque_type& >(value)));
+}
+
 template< typename To, typename From >
 BOOST_FORCEINLINE To bitwise_cast(From const& from) BOOST_NOEXCEPT
 {
@@ -39,8 +50,8 @@ BOOST_FORCEINLINE To bitwise_cast(From const& from) BOOST_NOEXCEPT
     value = {};
     BOOST_ATOMIC_DETAIL_MEMCPY
     (
-        &reinterpret_cast< char& >(value.to),
-        &reinterpret_cast< const char& >(from),
+        atomics::detail::addressof(value.to),
+        atomics::detail::addressof(from),
         (sizeof(From) < sizeof(To) ? sizeof(From) : sizeof(To))
     );
     return value.to;