regression, bisected: openpty fails from 3.7 onwards without devpts

[Florian Westphal <fw@strlen.de>]

Frank Lichtenheld discovered that openpty() doesn't work anymore when
/dev/pts is not present.

We bisected this down to

commit bbb63c514a3464342967237a51a21ea8f61ab951
Author: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Subject: drivers:tty:fix up ENOIOCTLCMD error handling

The original program triggering the error was pptpd, but
the test program below is sufficient:
----
#include <stdio.h>
#include <pty.h>
int main(void) {
 int pty_fd, tty_fd;
 if (openpty(&pty_fd, &tty_fd, NULL, NULL, NULL) != 0) {
  perror("openpty");
  return 1;
 }
return 0;
}
----
[ compile with cc -lutil pty.c -o pty ]

If devpts is available or above commit reverted openpty works again.