support pipe2 on BSD

[oconnor663]

Right now it's only available in the notbsd subtree, but it looks like the BSD's support it?

https://www.freebsd.org/cgi/man.cgi?query=pipe&sektion=2
http://netbsd.gw.com/cgi-bin/man-cgi?pipe2+2+NetBSD-current
http://man.openbsd.org/pipe.2

I might try moving it up to src/unix/mod.rs in a PR just to see what happens. Maybe Apple doesn't support it? Let me know if there's an easy way to figure this out without just seeing what breaks :)

[oconnor663]

Yep, it breaks on OSX. Would the right thing to do be to individually add it to the other BSD flavors?

[oconnor663]

Related question: nix currently hardcodes the platforms that support this call, https://github.com/nix-rust/nix/blob/master/src/unistd.rs#L617-L619. If we add more platforms, nix will want to update those lines. Is there a way for nix to avoid this kind of hardcoding?

[alexcrichton]

AFAIK there's no way to avoid hardcoding down the road, but yeah you can just add it to the BSD modules

[oconnor663]

Closing since #502 has landed.