Introduce protype-style function definition for S390 pthread_once.  The

old-style function definition was removed upstream in:

commit bc89c0fc70ba952f78fc27fc261ec209be0a6732

Author: Torvald Riegel <triegel@redhat.com>

Date:   Mon Dec 8 18:32:14 2014 +0100

    Remove custom pthread_once implementation on s390.

diff --git a/nptl/sysdeps/unix/sysv/linux/s390/pthread_once.c b/nptl/sysdeps/unix/sysv/linux/s390/pthread_once.c

index cd53d77c163661c5..4bce7fec13ea3bb2 100644

--- a/nptl/sysdeps/unix/sysv/linux/s390/pthread_once.c

+++ b/nptl/sysdeps/unix/sysv/linux/s390/pthread_once.c

@@ -34,9 +34,7 @@ clear_once_control (void *arg)

 int

-__pthread_once (once_control, init_routine)

-     pthread_once_t *once_control;

-     void (*init_routine) (void);

+__pthread_once (pthread_once_t *once_control, void (*init_routine) (void))

 {

   while (1)

     {