The file arc4random.c is removed in post-extract as everything is
implemented in OpenBSD libc.  Avoid a build warning about manifest.

--- MANIFEST.orig	Sun May 17 15:05:04 2009
+++ MANIFEST	Wed Oct 12 14:09:10 2016
@@ -3,7 +3,6 @@ META.yml
 Makefile.PL
 README
 TODO
-arc4random.c
 arc4rnd_xs.c
 lib/BSD/arc4random.pm
 t/check.t