vm_args.c (rb_warn_check): Use iseq_unique_id instead of its pointer

If iseq is GC'ed, the pointer of iseq may be reused, which may hide a
deprecation warning of keyword argument change.

http://ci.rvm.jp/results/trunk-test1@phosphorus-docker/2474221

```
  1) Failure:
TestKeywordArguments#test_explicit_super_kwsplat [/tmp/ruby/v2/src/trunk-test1/test/ruby/test_keyword.rb:549]:
--- expected
+++ actual
@@ -1 +1 @@
-/The keyword argument is passed as the last hash parameter.* for `m'/m
+""
```

This change ad-hocly adds iseq_unique_id for each iseq, and use it
instead of iseq pointer.  This covers the case where caller is GC'ed.
Still, the case where callee is GC'ed, is not covered.

But anyway, it is very rare that iseq is GC'ed.  Even when it occurs, it
just hides some warnings.  It's no big deal.

1 files changed, 3 insertions, 0 deletions

diff --git a/iseq.c b/iseq.c
index 7fbb906525..b3c7ad53d3 100644
--- a/iseq.c
+++ b/iseq.c
@@ -427,11 +427,14 @@ rb_iseq_memsize(const rb_iseq_t *iseq)
     return size;
 }
 
+static unsigned long fresh_iseq_unique_id = 0; /* -- Remove In 3.0 -- */
+
 static rb_iseq_t *
 iseq_alloc(void)
 {
     rb_iseq_t *iseq = iseq_imemo_alloc();
     iseq->body = ZALLOC(struct rb_iseq_constant_body);
+    iseq->body->iseq_unique_id = fresh_iseq_unique_id++; /* -- Remove In 3.0 -- */
     return iseq;
 }