Add support for Power (ppc64, ppc64le) and System z (s390x)

This PR add support for Power systems (ppc64, ppc64le) and System z (s390x).

We are working on porting Docker to Power and System z, and pty is an essential component for it.

Signed-off-by: Yohei Ueda <yohei@jp.ibm.com>