Add includes and split off json_types.h to help ensure that headers can be included in any order.

strerror_override_private.h

@@ -6,6 +6,8 @@
  * @brief Do not use, json-c internal, may be changed or removed at any time.
  */
 
+#include "json_types.h"
+
 /* Used by tests to get consistent output */
 JSON_EXPORT int _json_c_strerror_enable;