Add flist sorting

Imported from the kernel implementation.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/Makefile b/Makefile
index 837f421..978f8b2 100644
--- a/Makefile
+++ b/Makefile
@@ -10,6 +10,7 @@
 	cgroup.o profile.o debug.o
 
 OBJS += lib/rand.o
+OBJS += lib/flist_sort.o
 
 OBJS += crc/crc7.o
 OBJS += crc/crc16.o