configure: argp-standalone is always built, even when not needed

This patch still configures argp, i.e. creates Makefile in
/contrib/argp-standalone, for the `make dist`, but there's no reason
to compile it when it's not going to be linked into anything.

Change-Id: Id0fcb717b5821d8a4c176e6274339f46b3a4a249
BUG: 1086773
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/7440
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>