Allow obsoluted `MRB_METHOD_T_STRUCT`
MODIFY
include/mrbconf.h
include/mrbconf.h
//#define MRB_USE_ALL_SYMBOLS /* Symbol.all_symbols */
/* obsolete configurations */
+#ifdef MRB_METHOD_T_STRUCT
+# define MRB_USE_METHOD_T_STRUCT
+#endif
#if defined(DISABLE_STDIO) || defined(MRB_DISABLE_STDIO)
# define MRB_NO_STDIO
#endif

Allow obsoluted `MRB_METHOD_T_STRUCT`