ar: diff reduction against ELF Tool Chain

• Drop exit status from bsdar_errc. ELF Tool Chain always returns EXIT_FAILURE in bsdar_errc.

• Remove ar_mode_* wrappers and call ar_read_archive / ar_write_archive directly.

Obtained from: ELF Tool Chain
Reviewed by: markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31496

(cherry picked from commit d20e9e02db3dde383c3de1ce8cec3a8c35b3eee6)
(cherry picked from commit c5bf58add0d523fc6e6546f3fc10d0c8b972e8e7)
(cherry picked from commit 086f09087713e3af0a28d296a2372071b72211ef)
(cherry picked from commit 57aaefdceccdd590f81af4b274c7a3ee61ae62f1)
(cherry picked from commit 866c807472619371adcb2a0409a9287748a52654)