argp: avoid memory leak

argp: avoid memory leak

argp has been leaking memory since commit 79c0a43, in Jul 2006.

* modules/argp (Depends-on): Use dirname-lgpl, not dirname.
* lib/argp-namefrob.h (__argp_base_name): Use last_component, not
base_name, since the latter malloc()s and can call exit().

Signed-off-by: Eric Blake <ebb9@byu.net>