Portable ioctl calls

Add _IOC macros (<sys/ioccom.h>, <asm-generic/ioctl.h>) for linux and bsd's, unify ioctl() calls.
FreeBSD: use modern pts(4) interface instead of the old pty(4) one.
Use cgo -godefs generated ztypes_GOOS_GOARCH.go approach as in the syscall package to handle native C types.