Fix VC6 compilation after r61919.

Work around VC6 bug which resulted in error C2639 when compiling the
declaration of an unnamed struct inside wxGridCellAttrProvider.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61922 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/grid.h

@@ -567,6 +567,9 @@ private:
     wxGridCellAttrProviderData *m_data;
 
     // this struct simply combines together the default header renderers
+    //
+    // FIXME-VC6: this struct must be named because of VC6 bug, it fails
+    //            with error C2639 on this struct declaration without it
     struct
     {
         wxGridColumnHeaderRendererDefault colRenderer;