define operator<<(wxFileOffset) for VC6 only, it breaks compilation for at least wxMac

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@56165 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

tests/streams/fileback.cpp

@@ -19,13 +19,14 @@
 #endif
 
 
+#ifdef __VISUALC6__
 // need this to be able to use CPPUNIT_ASSERT_EQUAL with wxFileOffset objects
 static std::ostream& operator<<(std::ostream& ostr, const wxFileOffset& fo)
 {
     ostr << fo;
     return ostr;
 }
-
+#endif // VC++ 6
 
 #include "wx/mstream.h"
 #include "wx/private/fileback.h"