bug#42059: 26.3; OpenBSD now has posix_openpt(3)

[YASUOKA Masahiko <yasuoka@yasuoka.net>]

OpenBSD now has posix_openpt(3), emacs should use that.
A diff is attached.

Currently emacs uses an old way which actually causes a problem.  I am
using gnupg through Mew(*1) which run on emacs, Mew seems to create a
process without a pty regardless it specifies "process-connection-type
pty" properly.  The pty is required to pass the passphrase.

*1) http://mew.org/


--- configure.ac.orig	Fri Jun 26 18:33:33 2020
+++ configure.ac	Thu Aug 22 07:25:23 2019
@@ -4620,11 +4620,11 @@ case $opsys in
     AC_DEFINE(PTY_TTY_NAME_SPRINTF, [])
     ;;
 
-  gnu | qnxnto )
+  gnu | openbsd | qnxnto )
     AC_DEFINE(FIRST_PTY_LETTER, ['p'])
     ;;
 
-  gnu-linux | gnu-kfreebsd | dragonfly | freebsd | openbsd | netbsd | darwin | nacl )
+  gnu-linux | gnu-kfreebsd | dragonfly | freebsd | netbsd | darwin | nacl )
     dnl if HAVE_GRANTPT
     if test "x$ac_cv_func_grantpt" = xyes; then
       AC_DEFINE(UNIX98_PTYS, 1, [Define if the system has Unix98 PTYs.])


Configured using:
 'configure --build=amd64-unknown-openbsd --without-sound
 --with-x-toolkit=gtk3 --prefix=/usr/local --sysconfdir=/etc
 --mandir=/usr/local/man --infodir=/usr/local/info
 --localstatedir=/var --disable-silent-rules --disable-gtk-doc
 'CFLAGS=-O2 -pipe -g -fno-pie' CPPFLAGS=-I/usr/local/include
 'LDFLAGS=-L/usr/local/lib -nopie -g''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK DBUS GSETTINGS GLIB NOTIFY
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 XDBE XIM THREADS LCMS2

Important settings:
  value of $LC_CTYPE: ja_JP.UTF-8
  value of $LANG: ja_JP.UTF-8
  value of $XMODIFIERS: 
  locale-coding-system: utf-8-unix

Major mode: Summary

Minor modes in effect:
  diff-auto-refine-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow emacsbug message rmc puny seq byte-opt gv bytecomp
byte-compile cconv dired dired-loaddefs format-spec rfc822 mml mml-sec
password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils misearch multi-isearch anthy-conf
anthy-dic anthy vc-git diff-mode easy-mmode pp qp mew-varsx mew-unix
mew-auth mew-config mew-imap2 mew-imap mew-nntp2 mew-nntp mew-pop
mew-smtp mew-ssl mew-ssh mew-net mew-highlight mew-sort mew-fib
mew-ext mew-refile mew-demo mew-attach mew-draft mew-message
mew-thread mew-virtual mew-summary4 mew-summary3 mew-summary2
mew-summary mew-search mew-pick mew-passwd mew-scan mew-syntax mew-bq
mew-smime mew-pgp mew-header mew-exec mew-mark mew-mime mew-edit
mew-decode mew-encode mew-cache mew-minibuf mew-complete mew-addrbook
mew-local mew-vars3 mew-vars2 mew-vars mew-env mew-lang-jp mew-mule3
mew-mule mew-gemacs easymenu mew-key mew-func mew-blvs mew-const mew
elec-pair edmacro kmacro cl-loaddefs cl-lib time-date mule-util
japan-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite charscript
charprop case-table epa-hook jka-cmpr-hook help simple abbrev obarray
minibuffer cl-preloaded nadvice loaddefs button faces cus-face
macroexp files text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget hashtable-print-readable backquote
threads dbusbind kqueue lcms2 dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 166712 13664)
 (symbols 48 26580 2)
 (miscs 40 396 845)
 (strings 32 50253 1145)
 (string-bytes 1 1271766)
 (vectors 16 22102)
 (vector-slots 8 838358 23398)
 (floats 8 79 319)
 (intervals 56 3324 0)
 (buffers 992 16))