Detail: Fix BOOST_CONTAINER_FWD_COMPLEX_STRUCT. Refs #6139.

My last change was wrong, it isn't struct for Dinkumware. In GCC's
standard library it's declared as a class, but later defined as a
struct. This is so far untested as I'm building the latest trunk version
of clang (the warning doesn't show for the current clang release).

[SVN r75600]

include/boost/detail/container_fwd.hpp

@@ -42,6 +42,10 @@
         || defined(_GLIBCXX_PARALLEL) \
         || defined(_GLIBCXX_PROFILE)
 #      define BOOST_DETAIL_NO_CONTAINER_FWD
+#    else
+#      if defined(__GLIBCXX__) && __GLIBCXX__ >= 20040530
+#        define BOOST_CONTAINER_FWD_COMPLEX_STRUCT
+#      endif
 #    endif
 #  elif defined(__STL_CONFIG_H)
      // generic SGI STL
@@ -63,7 +67,6 @@
 #  elif (defined(_YVALS) && !defined(__IBMCPP__)) || defined(_CPPLIB_VER)
      // Dinkumware Library (this has to appear after any possible replacement
      // libraries)
-#    define BOOST_CONTAINER_FWD_COMPLEX_STRUCT
 #  else
 #    define BOOST_DETAIL_NO_CONTAINER_FWD
 #  endif