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

commit 7729e0e91afbf8d45bb322d7e2d53f417fab01ed
Author: Alexandre Oliva <aoliva@redhat.com>
Date:   Fri Nov 21 02:06:22 2014 -0200

    ctermid: return string literal, document MT-Safety pitfall

diff --git a/sysdeps/posix/ctermid.c b/sysdeps/posix/ctermid.c
index 8a0ebac8afaf23ff..94c0a6d25a5b430e 100644
--- a/sysdeps/posix/ctermid.c
+++ b/sysdeps/posix/ctermid.c
@@ -23,8 +23,7 @@
    If S is not NULL, the name is copied into it (it should be at
    least L_ctermid bytes long), otherwise a static buffer is used.  */
 char *
-ctermid (s)
-     char *s;
+ctermid (char *s)
 {
   static char name[L_ctermid];