Define arguments forwarding as `ruby2_keywords` style

Get rid of these redundant and useless warnings.

```
$ ruby -e 'def bar(a) a; end; def foo(...) bar(...) end; foo({})'
-e:1: warning: The last argument is used as the keyword parameter
-e:1: warning: for `foo' defined here
-e:1: warning: The keyword argument is passed as the last hash parameter
-e:1: warning: for `bar' defined here
```

1 files changed, 1 insertions, 0 deletions

diff --git a/compile.c b/compile.c
index 0440ec5fbc..278736d1b1 100644
--- a/compile.c
+++ b/compile.c
@@ -1650,6 +1650,7 @@ iseq_set_arguments(rb_iseq_t *iseq, LINK_ANCHOR *const optargs, const NODE *cons
 
 	EXPECT_NODE("iseq_set_arguments", node_args, NODE_ARGS, COMPILE_NG);
 
+        body->param.flags.ruby2_keywords = args->ruby2_keywords;
 	body->param.lead_num = arg_size = (int)args->pre_args_num;
 	if (body->param.lead_num > 0) body->param.flags.has_lead = TRUE;
 	debugs("  - argc: %d\n", body->param.lead_num);