For a test case such as: ```C++ extern struct { int a; } /// A test variable named 'y' y; ``` How to mark the unnamed class as implementation defined? Right now, this requires adding an entry to the configuration with the name of the class. We could either: * Give the class a legible name and make this work with that. * Support some kind of marker attached to the class, such as: ```/// implementation-defined``` * Require the user to provide a name in this case.