common/rc: fix unicode checker detection in xfs_scrub

common/rc: fix unicode checker detection in xfs_scrub

_check_xfs_scrub_does_unicode is still less than adequate -- if running
ldd to report the xfs_scrub binary's dynamic library dependencies
doesn't work, we could still detect support by grepping for strings that
only appear when the unicode checker is built.

Note that this isn't the final word on all of this; I will make this
easier to discover in a future xfs_scrub release.

Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>