xfs: repair superblocks

If one of the backup superblocks is found to differ seriously from
superblock 0, write out a fresh copy from the in-core sb.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
index d734445..e8d67a4 100644
--- a/fs/xfs/Makefile
+++ b/fs/xfs/Makefile
@@ -168,6 +168,7 @@
 # online repair
 ifeq ($(CONFIG_XFS_ONLINE_REPAIR),y)
 xfs-y				+= $(addprefix scrub/, \
+				   agheader_repair.o \
 				   repair.o \
 				   )
 endif