upstream OpenBSD: arc4random: replace abort() with _exit()

In the incredibly unbelievable circumstance where _rs_init() fails to
allocate pages, don't call abort() because of corefile data leakage
concerns, but simply _exit(). The reasoning is _rs_init() will only fail
if someone finds a way to apply specific pressure against this failure
point, for the purpose of leaking information into a core which they can
read. We don't need a corefile in this instance to debug that. So take
this "lever" away from whoever in the future wants to do that.

newlib/libc/stdlib/arc4random.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: arc4random.c,v 1.54 2015/09/13 08:31:47 guenther Exp $	*/
+/*	$OpenBSD: arc4random.c,v 1.55 2019/03/24 17:56:54 deraadt Exp $	*/
 
 /*
  * Copyright (c) 1996, David Mazieres <dm@uun.org>
@@ -75,7 +75,7 @@ _rs_init(u_char *buf, size_t n)
 
 	if (rs == NULL) {
 		if (_rs_allocate(&rs, &rsx) == -1)
-			abort();
+			_exit(1);
 	}
 
 	chacha_keysetup(&rsx->rs_chacha, buf, KEYSZ * 8, 0);