Add support for illumos target

[pfmooney]

As the master branch counterpart to the 0.6.x PR (#1294), this adds support for the Solaris-like (but distinct) illumos target. When support is merged into rust, it would be nice for mio to be immediately usable.

[Thomasdezeeuw]

Does this need a bump in libc version? I can image there will be changes required to that crate as well.

Also we would need CI support, running at least cargo check, for Illumos to be supported by Mio.

[pfmooney]

Does this need a bump in libc version? I can image there will be changes required to that crate as well.

Yep, fixed.

Also we would need CI support, running at least cargo check, for Illumos to be supported by Mio.

I'm waiting on the PR to add support for the target into rustc right now. I have tested locally with a toolchain built from that to ensure that the results compile (and pass at least as many tests as the x86_64-sun-solaris target does). Considering that the illumos triple is going to effectively subsume many (most?) instances of the solaris one, we wanted to get ahead of it so popular crates like mio will be supported ASAP once support shows up in nightly builds.

[Thomasdezeeuw]

LGTM, I think this is blocked on #1301 with the CI waiting for ever.

[kleimkuhler]

This looks good once it is rebased.

[pfmooney]

This looks good once it is rebased.

Rebased, with the conflicts addressed.

[Thomasdezeeuw]

@pfmooney thanks!