Change default `mrb_value` representation to `MRB_WORD_BOXING`.
/* if no specific boxing type is chosen */
#if !defined(MRB_NAN_BOXING) && !defined(MRB_WORD_BOXING) && !defined(MRB_NO_BOXING)
-# if defined(MRB_64BIT) && !defined(MRB_INT64)
-# define MRB_NAN_BOXING
-# else
# define MRB_WORD_BOXING
#endif
-#endif
/* add -DMRB_INT32 to use 32bit integer for mrb_int; conflict with MRB_INT64;
Default for 32-bit CPU mode. */
