load_exec(): Fix message lenghtes in mrb_exc_new().

mrb_run(): Fix not to use a magic number but sizeof.

src/parse.y

@@ -4875,7 +4875,8 @@ load_exec(mrb_state *mrb, parser_state *p, mrbc_context *c)
       return mrb_undef_value();
     }
     else {
-      mrb->exc = (struct RObject*)mrb_object(mrb_exc_new(mrb, E_SYNTAX_ERROR, "syntax error", 0));
+      static const char msg[] = "syntax error";
+      mrb->exc = (struct RObject*)mrb_object(mrb_exc_new(mrb, E_SYNTAX_ERROR, msg, sizeof(msg) - 1));
       mrb_parser_free(p);
       return mrb_nil_value();
     }
@@ -4883,7 +4884,8 @@ load_exec(mrb_state *mrb, parser_state *p, mrbc_context *c)
   n = mrb_generate_code(mrb, p->tree);
   mrb_parser_free(p);
   if (n < 0) {
-    mrb->exc = (struct RObject*)mrb_object(mrb_exc_new(mrb, E_SCRIPT_ERROR, "codegen error", 0));
+    static const char msg[] = "codegen error";
+    mrb->exc = (struct RObject*)mrb_object(mrb_exc_new(mrb, E_SCRIPT_ERROR, msg, sizeof(msg) - 1));
     return mrb_nil_value();
   }
   if (c) {

src/vm.c

@@ -1598,7 +1598,8 @@ mrb_run(mrb_state *mrb, struct RProc *proc, mrb_value self)
     CASE(OP_TCLASS) {
       /* A B    R(A) := target_class */
       if (!mrb->ci->target_class) {
-	mrb_value exc = mrb_exc_new(mrb, E_TYPE_ERROR, "no target class or module", 25);
+        static const char msg[] = "no target class or module";
+        mrb_value exc = mrb_exc_new(mrb, E_TYPE_ERROR, msg, sizeof(msg) - 1);
         mrb->exc = (struct RObject*)mrb_object(exc);
         goto L_RAISE;
       }