The invocation changed, follow the changes.
Move the test at its right place
Adapt to the new invocation.
Implement diagnostic report in missing .x function to call.
Use #include instead of real files.

If we use real files cling would .x them and run a function named after the file.
In our case it is missing and would issue useless warnings.
Print fwd decls for full class template specializations, and printStats for ForwardDeclPrinter