LU-1077 distribute missing file in build/autoconf

In landing 0d5cf708f60c1ed9233fd12f4326851ab412ef6a for ticket
LU-723 a defect was introduced where
build/autoconf/lustre-build-ldiskfs.m4 is missing from the
distribution tarball.

Signed-off-by: Brian J. Murrell <brian@whamcloud.com>
Change-Id: I34a1d7ad20229fb531eb4e76182647e708b300d4
Reviewed-on: http://review.whamcloud.com/2115
Tested-by: Hudson
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Prakash Surya <surya1@llnl.gov>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>