OpenSSL crypto backend: suppress deprecation warnings.

The old API is still supported and because we support very old
OpenSSL, this is the best wrokaround for the warnings.

Once we switch to the new OpenSSL version requirement, we can rewrite
HMAC to new EVP_MAC API.

lib/crypto_backend/crypto_openssl.c

@@ -28,6 +28,11 @@
  * for all of the code used other than OpenSSL.
  */
 
+/*
+ * HMAC will be later rewritten to a new API from OpenSSL 3
+ */
+#define OPENSSL_SUPPRESS_DEPRECATED
+
 #include <string.h>
 #include <errno.h>
 #include <openssl/evp.h>