libc: revert inadvertent removal of O_CLOEXEC #ifndefs

Change-Id: I15005181388280363f7aee546bd2ecc0cd5b37e6

lib/libc/gen/initdir.c

@@ -42,6 +42,10 @@ __RCSID("$NetBSD: initdir.c,v 1.3 2012/03/13 21:13:36 christos Exp $");
 #include <sys/featuretest.h>
 #include <sys/types.h>
 
+#ifndef O_CLOEXEC
+#define O_CLOEXEC 0
+#endif
+
 #endif
 
 #include "reentrant.h"