type of mrb_type() should be enum mrb_vtype when MRB_NAN_BOXING is on

include/mruby/value.h

@@ -158,7 +158,7 @@ typedef struct mrb_value {
  * In order to get enough bit size to save TT, all pointers are shifted 2 bits
  * in the right direction.
  */
-#define mrb_tt(o)       (((o).value.ttt & 0xfc000)>>14)
+#define mrb_tt(o)       ((enum mrb_vtype)(((o).value.ttt & 0xfc000)>>14))
 #define mrb_mktt(tt)    (0xfff00000|((tt)<<14))
 #define mrb_type(o)     ((uint32_t)0xfff00000 < (o).value.ttt ? mrb_tt(o) : MRB_TT_FLOAT)
 #define mrb_ptr(o)      ((void*)((((uintptr_t)0x3fffffffffff)&((uintptr_t)((o).value.p)))<<2))