node.c: Fix possible alignment bugs

* node.c (rb_node_buffer_new): Use offsetof for
  node_buffer_t size calculation.
* node.c (rb_ast_newnode): Use offsetof for
  node_buffer_elem_t size calculation.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60628 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

node.c

@@ -1235,7 +1235,7 @@ struct node_buffer_struct {
 node_buffer_t *
 rb_node_buffer_new()
 {
-    node_buffer_t *nb = xmalloc(sizeof(node_buffer_t) + 16 * sizeof(NODE));
+    node_buffer_t *nb = xmalloc(offsetof(node_buffer_t, body) + offsetof(node_buffer_elem_t, buf) + 16 * sizeof(NODE));
     nb->idx = 0;
     nb->len = 16;
     nb->head = &nb->body;
@@ -1263,7 +1263,7 @@ rb_ast_newnode(rb_ast_t *ast)
     if (nb->idx >= nb->len) {
 	long n = nb->len * 2;
 	node_buffer_elem_t *nbe;
-	nbe = xmalloc(sizeof(node_buffer_elem_t) + n * sizeof(NODE));
+	nbe = xmalloc(offsetof(node_buffer_elem_t, buf) + n * sizeof(NODE));
 	nb->idx = 0;
 	nb->len = n;
 	nbe->next = nb->head;