c2ffi handling va_list

[Madhu]

one of the cffi/TODO items has
-> Handle va_list. For now it's treated as any other argument.

Maybe someone has thought deeply about how to do this?  Please let me
know if you have any suggestions.

[It seems borodust/claw tries to handle this by converting va_list
args to variadic lisp arguments - but it still seems to blow up at a
cffi:parse-type.  Or maybe it is a defect with my Clang-7.0 stdarg
vs. what is included with gcc]