termios package does not compile under OpenBSD, NetBSD or DragonflyBSD

[driusan]

The termios/pty_bsd.go build tags build the file for FreeBSD, NetBSD and OpenBSD, but two of the syscall constants that it refers to (syscall.SYS_POSIX_OPENPT and syscall.TIOCGPTN) are only defined for FreeBSD if you grep the syscall package source.

In addition to this, the BSD variant files are missing build tags for DragonflyBSD.

[mndrix]

I think I've fixed this in pull request #30. I know it works on OpenBSD. If anyone has access to FreeBSD, DragonFly BSD and NetBSD, I'd appreciate any testing you could do there.

[iquiw]

I tested it with go version go1.10.1 netbsd/386 on NetBSD 8.0_RC1 and go version go1.10.1 netbsd/amd64 on NetBSD current (8.99.14).
Both go build and go test succeeded.

[gdamore]

I think this issue should be closed. Builds for those platforms seem to work for me.