new helper: sigsuspend()

guts of saved_sigmask-based sigsuspend/rt_sigsuspend.  Takes
kernel sigset_t *.

Open-coded instances replaced with calling it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index 8a4e2b7..f626232 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -59,15 +59,8 @@
 SYSCALL_DEFINE3(sigsuspend, int, history0, int, history1, old_sigset_t, mask)
 {
 	sigset_t blocked;
-
-	current->saved_sigmask = current->blocked;
-	mask &= _BLOCKABLE;
 	siginitset(&blocked, mask);
-	set_current_blocked(&blocked);
-	set_current_state(TASK_INTERRUPTIBLE);
-	schedule();
-	set_restore_sigmask();
-	return -ERESTARTNOHAND;
+	return sigsuspend(&blocked);
 }
 
 SYSCALL_DEFINE3(sigaction, int, sig, const struct old_sigaction __user *, act,