LU-8837 target: don't build any 'target' on client.

LU-8837 target: don't build any 'target' on client.

Nothing in the 'target/' directory is needed on the client,
so don't build it for client-only builds

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I9a63c1a11c7b44edadc355bd323381ba1951376f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/41768
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>