use memset_s

lib roken includes support for memset_s() but it was not applied
to the Heimdal source tree.

Change-Id: I8362ec97a9be50205bb2d398e65b629b88ce1acd

lib/krb5/deprecated.c

@@ -207,7 +207,7 @@ krb5_password_key_proc (krb5_context context,
 	password = buf;
     }
     ret = krb5_string_to_key_salt (context, type, password, salt, *key);
-    memset (buf, 0, sizeof(buf));
+    memset_s(buf, sizeof(buf), 0, sizeof(buf));
     return ret;
 }