[S390] duplicate SIGTRAP on signal delivery.

The code in do_signal sets the TIF_SINGLE_STEP bit and calls
tracehook_signal_handler after the signal frame has been set up.
This causes two SIGTRAP signals to be delivered to the tracer.
Stop setting the TIF_SINGLE_STEP bit in do_signal to get the
correct number of SIGTRAPs.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/signal.c

@@ -499,19 +499,11 @@ void do_signal(struct pt_regs *regs)
 			if (test_thread_flag(TIF_RESTORE_SIGMASK))
 				clear_thread_flag(TIF_RESTORE_SIGMASK);
 
-			/*
-			 * If we would have taken a single-step trap
-			 * for a normal instruction, act like we took
-			 * one for the handler setup.
-			 */
-			if (current->thread.per_info.single_step)
-				set_thread_flag(TIF_SINGLE_STEP);
-
 			/*
 			 * Let tracing know that we've done the handler setup.
 			 */
 			tracehook_signal_handler(signr, &info, &ka, regs,
-					 test_thread_flag(TIF_SINGLE_STEP));
+					current->thread.per_info.single_step);
 		}
 		return;
 	}