should not free() static iseq from cdump

include/mruby/irep.h

@@ -12,10 +12,10 @@ extern "C" {
 #endif
 
 typedef struct mrb_irep {
-  int idx;
-
-  int nlocals;
-  int nregs;
+  int idx:16;
+  int nlocals:16;
+  int nregs:16;
+  int flags:8;
 
   mrb_code *iseq;
   mrb_value *pool;
@@ -28,6 +28,8 @@ typedef struct mrb_irep {
   int ilen, plen, slen;
 } mrb_irep;
 
+#define MRB_ISEQ_NO_FREE 1
+
 void mrb_add_irep(mrb_state *mrb, int n);
 
 #if defined(__cplusplus)