Make the termp and winp arguments for openpty, et al. const.

This matches the prototypes in glibc and musl libc.
From Matthew Martin. OK tb@

Author: millert

lib/libutil/openpty.3

@@ -1,4 +1,4 @@
-.\"	$OpenBSD: openpty.3,v 1.19 2017/04/20 19:30:42 jmc Exp $
+.\"	$OpenBSD: openpty.3,v 1.20 2022/04/20 14:00:19 millert Exp $
 .\" Copyright (c) 1995
 .\"	The Regents of the University of California.  All rights reserved.
 .\"
@@ -30,7 +30,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: April 20 2017 $
+.Dd $Mdocdate: April 20 2022 $
 .Dt OPENPTY 3
 .Os
 .Sh NAME
@@ -47,15 +47,15 @@
 .Ft int
 .Fn getptmfd "void"
 .Ft int
-.Fn openpty "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp"
+.Fn openpty "int *amaster" "int *aslave" "char *name" "const struct termios *termp" "const struct winsize *winp"
 .Ft int
-.Fn fdopenpty "int ptmfd" "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp"
+.Fn fdopenpty "int ptmfd" "int *amaster" "int *aslave" "char *name" "const struct termios *termp" "const struct winsize *winp"
 .Ft int
 .Fn login_tty "int fd"
 .Ft pid_t
-.Fn forkpty "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp"
+.Fn forkpty "int *amaster" "char *name" "const struct termios *termp" "const struct winsize *winp"
 .Ft pid_t
-.Fn fdforkpty "int ptmfd" "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp"
+.Fn fdforkpty "int ptmfd" "int *amaster" "char *name" "const struct termios *termp" "const struct winsize *winp"
 .Sh DESCRIPTION
 The
 .Fn openpty ,

lib/libutil/pty.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: pty.c,v 1.21 2017/04/20 17:48:30 nicm Exp $	*/
+/*	$OpenBSD: pty.c,v 1.22 2022/04/20 14:00:19 millert Exp $	*/
 
 /*-
  * Copyright (c) 1990, 1993
@@ -50,8 +50,8 @@ getptmfd(void)
 }
 
 int
-openpty(int *amaster, int *aslave, char *name, struct termios *termp,
-    struct winsize *winp)
+openpty(int *amaster, int *aslave, char *name, const struct termios *termp,
+    const struct winsize *winp)
 {
 	int ptmfd;
 
@@ -67,7 +67,7 @@ openpty(int *amaster, int *aslave, char *name, struct termios *termp,
 
 int
 fdopenpty(int ptmfd, int *amaster, int *aslave, char *name,
-    struct termios *termp, struct winsize *winp)
+    const struct termios *termp, const struct winsize *winp)
 {
 	int master, slave;
 	struct ptmget ptm;
@@ -97,7 +97,8 @@ fdopenpty(int ptmfd, int *amaster, int *aslave, char *name,
 }
 
 pid_t
-forkpty(int *amaster, char *name, struct termios *termp, struct winsize *winp)
+forkpty(int *amaster, char *name, const struct termios *termp,
+    const struct winsize *winp)
 {
 	int ptmfd;
 	pid_t pid;
@@ -113,8 +114,8 @@ forkpty(int *amaster, char *name, struct termios *termp, struct winsize *winp)
 }
 
 pid_t
-fdforkpty(int ptmfd, int *amaster, char *name, struct termios *termp,
-    struct winsize *winp)
+fdforkpty(int ptmfd, int *amaster, char *name, const struct termios *termp,
+    const struct winsize *winp)
 {
 	int master, slave;
 	pid_t pid;

lib/libutil/util.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: util.h,v 1.36 2019/08/30 03:57:56 deraadt Exp $	*/
+/*	$OpenBSD: util.h,v 1.37 2022/04/20 14:00:19 millert Exp $	*/
 /*	$NetBSD: util.h,v 1.2 1996/05/16 07:00:22 thorpej Exp $	*/
 
 /*-
@@ -99,12 +99,14 @@ void	pw_copy(int, int, const struct passwd *, const struct passwd *);
 int	pw_scan(char *, struct passwd *, int *);
 void	pw_error(const char *, int, int);
 int	getptmfd(void);
-int	openpty(int *, int *, char *, struct termios *, struct winsize *);
-int	fdopenpty(int, int *, int *, char *, struct termios *,
-	    struct winsize *);
+int	openpty(int *, int *, char *, const struct termios *,
+	    const struct winsize *);
+int	fdopenpty(int, int *, int *, char *, const struct termios *,
+	    const struct winsize *);
 int	opendisk(const char *, int, char *, size_t, int);
-pid_t	forkpty(int *, char *, struct termios *, struct winsize *);
-pid_t	fdforkpty(int, int *, char *, struct termios *, struct winsize *);
+pid_t	forkpty(int *, char *, const struct termios *, const struct winsize *);
+pid_t	fdforkpty(int, int *, char *, const struct termios *,
+	    const struct winsize *);
 int	getmaxpartitions(void);
 int	getrawpartition(void);
 void	login_fbtab(const char *, uid_t, gid_t);