os: ignore SIGTTIN during TestTTYClose

Otherwise, if the test is run in the background, it will stop waiting
for access to the terminal.

Change-Id: Ib5224c6cb9060281e05c3b00cd2964445421e774
Reviewed-on: https://go-review.googlesource.com/c/136415
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/timeout_test.go

@@ -16,8 +16,10 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"os"
+	"os/signal"
 	"runtime"
 	"sync"
+	"syscall"
 	"testing"
 	"time"
 )
@@ -591,6 +593,10 @@ func TestRacyWrite(t *testing.T) {
 
 // Closing a TTY while reading from it should not hang.  Issue 23943.
 func TestTTYClose(t *testing.T) {
+	// Ignore SIGTTIN in case we are running in the background.
+	signal.Ignore(syscall.SIGTTIN)
+	defer signal.Reset(syscall.SIGTTIN)
+
 	f, err := os.Open("/dev/tty")
 	if err != nil {
 		t.Skipf("skipping because opening /dev/tty failed: %v", err)