upstream: lots of things were relying on libcrypto headers to

transitively include various system headers (mostly stdlib.h); include them
explicitly

OpenBSD-Commit-ID: 5b522f4f2d844f78bf1cc4f3f4cc392e177b2080
diff --git a/auth2-chall.c b/auth2-chall.c
index 2d5cff4..671f2f0 100644
--- a/auth2-chall.c
+++ b/auth2-chall.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-chall.c,v 1.50 2018/07/11 18:55:11 markus Exp $ */
+/* $OpenBSD: auth2-chall.c,v 1.51 2019/09/06 04:53:27 djm Exp $ */
 /*
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
  * Copyright (c) 2001 Per Allansson.  All rights reserved.
@@ -28,6 +28,7 @@
 
 #include <sys/types.h>
 
+#include <stdlib.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <string.h>