os/signal: use syscall.Wait4 directly in tests

Rather than using syscall.Syscall6 with SYS_WAIT4, use syscall.Wait4
directly.

Updates #59667

Change-Id: I50fea3b7d10003dbc632aafd5e170a9fe96d6f42
Reviewed-on: https://go-review.googlesource.com/c/go/+/538459
Run-TryBot: Joel Sing <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

src/os/signal/signal_cgo_test.go

@@ -288,15 +288,14 @@ func runSessionLeader(t *testing.T, pause time.Duration) {
 
  // Wait for stop.
  var status syscall.WaitStatus
- var errno syscall.Errno
  for {
- _, _, errno = syscall.Syscall6(syscall.SYS_WAIT4, uintptr(cmd.Process.Pid), uintptr(unsafe.Pointer(&status)), syscall.WUNTRACED, 0, 0, 0)
- if errno != syscall.EINTR {
+ _, err = syscall.Wait4(cmd.Process.Pid, &status, syscall.WUNTRACED, nil)
+ if err != syscall.EINTR {
  break
  }
  }
- if errno != 0 {
- return fmt.Errorf("error waiting for stop: %w", errno)
+ if err != nil {
+ return fmt.Errorf("error waiting for stop: %w", err)
  }
 
  if !status.Stopped() {
@@ -305,7 +304,7 @@ func runSessionLeader(t *testing.T, pause time.Duration) {
 
  // Take TTY.
  pgrp := int32(syscall.Getpgrp()) // assume that pid_t is int32
- _, _, errno = syscall.Syscall(syscall.SYS_IOCTL, ptyFD, syscall.TIOCSPGRP, uintptr(unsafe.Pointer(&pgrp)))
+ _, _, errno := syscall.Syscall(syscall.SYS_IOCTL, ptyFD, syscall.TIOCSPGRP, uintptr(unsafe.Pointer(&pgrp)))
  if errno != 0 {
  return fmt.Errorf("error setting tty process group: %w", errno)
  }