unix: fix Pipe2 on dragonfly

The pipe2 on dragonfly still expects an fds array as an argument, but
does not use it to return the file descriptors. Just pass the argument
but ignore its value. This way the flags argument will be respected
correctly.

Change-Id: Id340653040999f31074eae01e9be4ea2088abae5
Reviewed-on: https://go-review.googlesource.com/c/sys/+/295870
Trust: Tobias Klauser <[email protected]>
Run-TryBot: Tobias Klauser <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: tklauser

unix/syscall_dragonfly.go

@@ -105,13 +105,16 @@ func Pipe(p []int) (err error) {
 	return
 }
 
-//sysnb	pipe2(flags int) (r int, w int, err error)
+//sysnb	pipe2(p *[2]_C_int, flags int) (r int, w int, err error)
 
 func Pipe2(p []int, flags int) (err error) {
 	if len(p) != 2 {
 		return EINVAL
 	}
-	p[0], p[1], err = pipe2(flags)
+	var pp [2]_C_int
+	// pipe2 on dragonfly takes an fds array as an argument, but still
+	// returns the file descriptors.
+	p[0], p[1], err = pipe2(&pp, flags)
 	return err
 }