Fix PTY.open on OpenBSD [Bug #15607]

From: Jeremy Evans <code@jeremyevans.net>

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67183 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/pty/pty.c

@@ -247,7 +247,7 @@ get_device_once(int *master, int *slave, char SlaveName[DEVICELEN], int nomesg,
     int masterfd = -1, slavefd = -1;
     char *slavedevice;
 
-#if defined(__sun) || (defined(__FreeBSD__) && __FreeBSD_version < 902000)
+#if defined(__sun) || defined(__OpenBSD__) || (defined(__FreeBSD__) && __FreeBSD_version < 902000)
     /* workaround for Solaris 10: grantpt() doesn't work if FD_CLOEXEC is set.  [ruby-dev:44688] */
     /* FreeBSD 9.2 or later supports O_CLOEXEC
      * http://www.freebsd.org/cgi/query-pr.cgi?pr=162374 */