MAPNIK_DECL only on __GNUC__ builds

ref: error C2491: 'mapnik::feature_style_processor<Processor>::prepare_layers': definition of dllimport function not allowed

include/mapnik/feature_style_processor.hpp

@@ -47,7 +47,11 @@ struct layer_rendering_material;
 enum eAttributeCollectionPolicy { DEFAULT = 0, COLLECT_ALL = 1 };
 
 template<typename Processor>
+#ifdef __GNUC__
 class MAPNIK_DECL feature_style_processor
+#else
+class feature_style_processor
+#endif
 {
   public:
     explicit feature_style_processor(Map const& m, double scale_factor = 1.0);