xfs_io: add crc32 self test

xfs_io: add crc32 self test

Add a self test for crc32c into xfs_io so that xfstests can check the
operation of the (potentially cross-compiled) package binaries by
isolating the self test code to a header file that can be included by
the build system self test and xfs_io.

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>