Fixed macro def expansion

Src/AST/Myc.Ast.MacroExpander.pas

@@ -259,8 +259,9 @@ function TMacroExpander.VisitMacroDefinition(const Node: IMacroDefinitionNode):
 begin
     // Register the macro in the current descriptor
     FCurrentDescriptor.DefineMacro(Node.Name.Name, Node);
-    // Remove the (defmacro ...) node from the AST; it's compile-time only.
-    Result := nil;
+
+    // Keep the node in the AST (for the visualizer).
+    Result := Node;
 end;
 
 function TMacroExpander.VisitFunctionCall(const Node: IFunctionCallNode): IAstNode;