libxfs: use crc32c slice-by-8 variant by default

libxfs: use crc32c slice-by-8 variant by default

The crc32c code used in xfsprogs was copied directly from the Linux
kernel.  However, that code selects slice-by-4 by default, which isn't
the fastest -- that's slice-by-8, which trades table size for speed.
Fix some makefile dependency problems and explicitly select the
algorithm we want.  With this patch applied, I see about a 10% drop in
CPU time running xfs_repair.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>