Fix an OS X build error with the PROGRESS_DEFINE_NODE macro.

Progress/ProgressNode.hh

@@ -179,7 +179,7 @@ private:
     (Progress::Node* _next) \
   { \
     static thread_local TYPE node(#OPRT, _next, \
-      Node::make_child_list(##__VA_ARGS__));\
+      Node::make_child_list( __VA_ARGS__ ));\
     return OPRT##_node = &node; \
   }