haiku: add openpty/forkpty, and link to libbsd.
haiku: add openpty/forkpty, and link to libbsd.

rust-lang/libc,rust-lang/libc,cactorium/libc,rust-lang-nursery/libc,cactorium/libc,cactorium/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,rust-lang/libc