Suppress deprecation warnings of MD5 from Xcode 11.1

ext/digest/md5/md5cc.h

 #define COMMON_DIGEST_FOR_OPENSSL 1
 #include <CommonCrypto/CommonDigest.h>
 
+#ifdef __clang__
+# pragma clang diagnostic ignored "-Wdeprecated-declarations"
+/* Suppress deprecation warnings of MD5 from Xcode 11.1 */
+/* Although we know MD5 is deprecated too, provide just for backward
+ * compatibility, as well as Apple does. */
+#endif
+
 #define MD5_BLOCK_LENGTH	CC_MD5_BLOCK_BYTES
 
 static DEFINE_UPDATE_FUNC_FOR_UINT(MD5)