new helper: signal_delivered()

Does block_sigmask() + tracehook_signal_handler();  called when
sigframe has been successfully built.  All architectures converted
to it; block_sigmask() itself is gone now (merged into this one).

I'm still not too happy with the signature, but that's a separate
story (IMO we need a structure that would contain signal number +
siginfo + k_sigaction, so that get_signal_to_deliver() would fill one,
signal_delivered(), handle_signal() and probably setup...frame() -
take one).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/powerpc/kernel/signal.c

@@ -148,11 +148,7 @@ static int do_signal(struct pt_regs *regs)
 
 	regs->trap = 0;
 	if (ret) {
-		block_sigmask(&ka, signr);
-		/*
-		 * Let tracing know that we've done the handler setup.
-		 */
-		tracehook_signal_handler(signr, &info, &ka, regs,
+		signal_delivered(signr, &info, &ka, regs,
 					 test_thread_flag(TIF_SINGLESTEP));
 	}