ig-c99: be verbose on basetype declarations

lm-c99/ig-c99.ysl2

@@ -153,8 +153,11 @@ tstylesheet {
     function "basetypes" {
         for "func:idl_get_basetypes()" {
             const "name", "name()";
-            if "func:c99_typename_of_idltype($name) != $name" {
-                | «func:typedef(func:c99_typename_of_idltype($name), $name)»
+            choose {
+                when "func:c99_typename_of_idltype($name) != $name"
+                    | «func:typedef(func:c99_typename_of_idltype($name), $name)»
+                otherwise
+                    | // no typedef required for idl-basetype: «$name»
             }
         }
     }