libclang: get objective-c interface cursor from implementation cursor

Hello, world!

I am trying to use libclang to determine the superclass that an Objective-C
method belongs to. I have a cursor representing an instance method
(CXCursor_ObjCInstanceMethodDecl). When I get the cursor's parent, I get a
cursor of kind CXCursor_ObjCImplementationDecl. I need to be able to get the
interface cursor from this last cursor in order to determine the method's
superclass. Is there a way to do this? Sorry if this is a dumb question.
If I print the AST using -ast-dump, I see that the ObjCImplementationDecl
cursor has a child cursor that references the interface declaration, but I
don't see this reflected when I use the libclang API. Any help would be
greatly appreciated. Thanks!