From Marco Jez, fix for gcc build.

include/osgIntrospection/ReflectionMacros

@@ -33,8 +33,8 @@ namespace osgIntrospection
     template<typename T>
     struct is_polymorphic
     {
-        class dummy1: public T { ~dummy1(); };
-        class dummy2: public T { virtual ~dummy2(); };
+        struct dummy1: T { dummy1(); ~dummy1(); };
+        struct dummy2: T { dummy2(); virtual ~dummy2(); };
         enum { value = sizeof(dummy1) == sizeof(dummy2) };
     };
 
@@ -1596,3 +1596,4 @@ struct BaseTypeConverters<x, reflected_type, true>
 
 #endif
 
+