confnames: align to trailing underscore

src/ctypesgen/expressions.py

@@ -230,7 +230,7 @@ def __init__(self, op, format, base, attribute):
         # Fortunately, the processor module does the same thing to
         # the struct member name.
         if self.attribute in keyword.kwlist:
-            self.attribute = "_" + self.attribute
+            self.attribute += "_"
 
     def visit(self, visitor):
         self.base.visit(visitor)