syscall: fix TestForeground for AIX

Syscall function can't be used on AIX. Therefore, Ioctl in
TestForeground must call raw_ioctl.

Change-Id: I96c3b52ee2d61073ae367028d4dfa926107402ba
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/175080
Trust: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>