Create /etc/unwind.

re-commit now that snapshots are over the bump.
OK deraadt

src/etc/mtree/4.4BSD.dist

@@ -1,4 +1,4 @@
-#	$OpenBSD: 4.4BSD.dist,v 1.305 2019/01/26 12:09:39 florian Exp $
+#	$OpenBSD: 4.4BSD.dist,v 1.306 2019/01/27 16:11:55 florian Exp $
 
 /set type=dir uname=root gname=wheel mode=0755
 
@@ -106,6 +106,13 @@ etc
         lib
         ..
     ..
+
+    # ./etc/unwind
+    unwind
+        trustanchor		gname=_unwind uname=root mode=0775
+        ..
+    ..
+
 ..
 
 # ./home