VC6 compilation fix (thanks buildbot)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@60602 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/dlgcmn.cpp

@@ -104,7 +104,9 @@ wxWindow *wxDialogBase::CheckIfCanBeUsedAsParent(wxWindow *parent) const
         return NULL;
     }
 
-    if ( parent == this )
+    // FIXME-VC6: this compiler requires an explicit const cast or it fails
+    //            with error C2446
+    if ( const_cast<const wxWindow *>(parent) == this )
     {
         // not sure if this can really happen but it doesn't hurt to guard
         // against this clearly invalid situation