Add a new file for constant-time functions

Signed-off-by: gabor-mezei-arm <gabor.mezei@arm.com>

library/CMakeLists.txt

@@ -24,6 +24,7 @@ set(src_crypto
     chachapoly.c
     cipher.c
     cipher_wrap.c
+    constant_time.c
     cmac.c
     ctr_drbg.c
     des.c

library/Makefile

@@ -84,6 +84,7 @@ OBJS_CRYPTO= \
 	     cipher.o \
 	     cipher_wrap.o \
 	     cmac.o \
+	     constant_time.o \
 	     ctr_drbg.o \
 	     des.o \
 	     dhm.o \

library/constant_time.c

@@ -0,0 +1,20 @@
+/**
+ *  Constant-time functions
+ *
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#include "common.h"