Omit mutex_tid member from default build.

Author: nascheme

Include/internal/pycore_interp_structs.h

@@ -566,8 +566,10 @@ struct types_state {
         managed_static_type_state initialized[_Py_MAX_MANAGED_STATIC_EXT_TYPES];
     } for_extensions;
     PyMutex mutex;
+#ifdef Py_GIL_DISABLED
     // used to check correct usage of the above mutex
     unsigned long long mutex_tid;
+#endif
 
     // Borrowed references to type objects whose
     // tp_version_tag % TYPE_VERSION_CACHE_SIZE