Where did you get your copy of GDB from? The standard Apple tools use LLDB, and have for a number of years. Getting GDB to work on modern Apple OS releases is going to be tricky. I strongly recommend that you use LLDB instead.
Share and Enjoy — Quinn “The Eskimo!” Apple Developer Relations, Developer Technical Support, Core OS/Hardware let myEmail = "eskimo" + "1" + "@apple.com"