Introduce prototype-style function definition for getttynam.  Upstream,
this was part of:

commit abccad04b4172d552dbdae948c0e567ba266ad76
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Jun 17 20:21:19 2015 +0000

    Fix ttyslot namespace (bug 18547).

diff --git a/misc/getttyent.c b/misc/getttyent.c
index 864f65f523de2522..018789a801b8b764 100644
--- a/misc/getttyent.c
+++ b/misc/getttyent.c
@@ -44,8 +44,7 @@ static char zapchar;
 static FILE *tf;
 
 struct ttyent *
-getttynam(tty)
-	const char *tty;
+getttynam (const char *tty)
 {
 	struct ttyent *t;