Add Linus' optimized sha1 hash for checksum

It does appear to be pretty fast.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/Makefile b/Makefile
index 99acec9..59e53a7 100644
--- a/Makefile
+++ b/Makefile
@@ -14,6 +14,7 @@
 OBJS += crc/crc32c.o
 OBJS += crc/crc32c-intel.o
 OBJS += crc/crc64.o
+OBJS += crc/sha1.o
 OBJS += crc/sha256.o
 OBJS += crc/sha512.o
 OBJS += crc/md5.o