[ruby/digest] Suppress md5 deprecation warnings by gcc as well as clang

https://github.com/ruby/digest/commit/76878e3201

ext/digest/md5/md5cc.h

@@ -1,8 +1,16 @@
 #define COMMON_DIGEST_FOR_OPENSSL 1
 #include <CommonCrypto/CommonDigest.h>
 
-#ifdef __clang__
-# pragma clang diagnostic ignored "-Wdeprecated-declarations"
+#ifdef __GNUC__
+# define RB_DIGEST_DIAGNOSTIC(compiler, op, flag) _Pragma(STRINGIZE(compiler diagnostic op flag))
+# ifdef RBIMPL_WARNING_IGNORED
+#   define RB_DIGEST_WARNING_IGNORED(flag) RBIMPL_WARNING_IGNORED(flag)
+# elif defined(__clang__)
+#   define RB_DIGEST_WARNING_IGNORED(flag) RB_DIGEST_DIAGNOSTIC(clang, ignored, #flag)
+# else /* __GNUC__ */
+#   define RB_DIGEST_WARNING_IGNORED(flag) RB_DIGEST_DIAGNOSTIC(GCC, ignored, #flag)
+# endif
+RB_DIGEST_WARNING_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. */