Improve use of &deprecated on functions.

- Don't report warnings on function definition if declaration is marked
  deprecated.
- Allow &deprecated to apply to a standalone function definition.

src/ID.cc

@@ -248,6 +248,16 @@ void ID::UpdateValAttrs()
 		}
 	}
 
+void ID::MakeDeprecated()
+	{
+	if ( IsDeprecated() )
+		return;
+
+	attr_list* attr = new attr_list;
+	attr->append(new Attr(ATTR_DEPRECATED));
+	AddAttrs(new Attributes(attr, Type(), false));
+	}
+
 void ID::AddAttrs(Attributes* a)
 	{
 	if ( attrs )