unix: add IoctlCtlInfo on darwin

For golang/go#41868

Change-Id: I0f4dbeacfe10b9614caf05633a1de3a98a1fc85f
Reviewed-on: https://go-review.googlesource.com/c/sys/+/262959
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>

unix/syscall_darwin.go

@@ -13,6 +13,7 @@
 package unix
 
 import (
+	"runtime"
 	"syscall"
 	"unsafe"
 )
@@ -257,6 +258,12 @@ func Kill(pid int, signum syscall.Signal) (err error) { return kill(pid, int(sig
 
 //sys	ioctl(fd int, req uint, arg uintptr) (err error)
 
+func IoctlCtlInfo(fd int, ctlInfo *CtlInfo) error {
+	err := ioctl(fd, CTLIOCGINFO, uintptr(unsafe.Pointer(ctlInfo)))
+	runtime.KeepAlive(ctlInfo)
+	return err
+}
+
 //sys   sysctl(mib []_C_int, old *byte, oldlen *uintptr, new *byte, newlen uintptr) (err error) = SYS_SYSCTL
 
 func Uname(uname *Utsname) error {