Set ARCHIVE_EXTRACT_SECURE_SYMLINKS and ARCHIVE_EXTRACT_SECURE_NODOTDOT
as in bsdtar to prevent extraction of archive entries whose pathnames
contain .. or whose target directory would be altered by a symlink.
Also disallow absolute pathnames.

We don't currently provide an option to disable this behaviour (as
bsdtar's -P does). It is unlikely to be a problem in practice for ar(1),
but the -P option is not currently used and available if we want to
consider it for this purpose.