Fix build with Borland C++ compiler.

Disable some parts of the code that this compiler had problems with. Add
parentheses to work around its bugs elsewhere.

Closes #12558.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66054 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/propgrid/propgridiface.h

@@ -1385,7 +1385,8 @@ private:
     {
         if ( !m_pState )
             return NULL;
-        return static_cast<const wxPropertyGrid*>(m_pState->GetGrid());
+
+        return m_pState->GetGrid();
     }
 
     friend class wxPropertyGrid;