Sort out the variables which belongs to 'mrb_callinfo' to improve 'cipush' performance.

include/mruby.h

@@ -57,14 +57,14 @@ typedef struct {
   struct RProc *proc;
   mrb_value *stackent;
   int nregs;
-  int argc;
+  int ridx;
+  int eidx;
+  struct REnv *env;
   mrb_code *pc;                 /* return address */
   mrb_code *err;                /* error position */
+  int argc;
   int acc;
   struct RClass *target_class;
-  int ridx;
-  int eidx;
-  struct REnv *env;
 } mrb_callinfo;
 
 enum mrb_fiber_state {