Add a new file for constant-time functions

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/library/Makefile b/library/Makefile
index 2ee3615..1abafe3 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -84,6 +84,7 @@
 	     cipher.o \
 	     cipher_wrap.o \
 	     cmac.o \
+	     constant_time.o \
 	     ctr_drbg.o \
 	     des.o \
 	     dhm.o \