Add IoctlGetInt/IoctlSetInt, IoctlGetTermios/IoctlSetTermios and
IoctlGetWinsize/IoctlSetWinsize on Darwin. These are similar to the
already existing implementations on Linux and Solaris.

Generated on Mac OS 10.11 (Darwin 15.6.0).

Change-Id: I2d4cc957c840836fcc2ccb71c67631420f4a2eb1
Reviewed-on: https://go-review.googlesource.com/52410Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>