core: Add meta command handler stubs to argparse.c.
* src/argparse.c (handle_meta_user): New stub. (handle_meta_force): New stub. (handle_meta_ignore): New stub. (handle_meta_echo): New. (handle_metacmd): New. (_gpgrt_argparse): Call meta command handler.
- GnuPG-bug-id: T4788
- Signed-off-by: Werner Koch <wk@gnupg.org>