First step at speeding up io_u rand refill

Makes it 3x faster here.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/Makefile b/Makefile
index 12042f4..837f421 100644
--- a/Makefile
+++ b/Makefile
@@ -9,6 +9,8 @@
 	rbtree.o diskutil.o fifo.o blktrace.o smalloc.o filehash.o helpers.o \
 	cgroup.o profile.o debug.o
 
+OBJS += lib/rand.o
+
 OBJS += crc/crc7.o
 OBJS += crc/crc16.o
 OBJS += crc/crc32.o