Make networking on Solaris/Illumos great again

Add fchown

add UTIME_OMIT, UTIME_NOW on linux

add truncate64/readdir64/openat64 on linux

add AT_* constants

Add FIONREAD for apple/b64

Adds the FIONREAD constant for macos/x86_64 machines.

add fdopendir

Solaris/Illumos: Add several more filio ioctls

MIO needs these

move *at family to unix

apparently supported on all platforms.

Get CI working again

A few changes have necessitated some updates on our end

A few changes have necessitated some updates on our end

MIO needs these

Add support for the `accept4` system call for FreeBSD* & NetBSD*

As outlined in #540.

However since support for this system call seems to be committed, but not yet released in NetBSD & BitRig (is BitRig actually still be developed at all, btw?), I'm not sure whether it wouldn't be a better idea to only add OpenBSD support instead?
What's the official policy on this?

Bump to 0.2.21

closes https://github.com/rust-lang/libc/issues/539

closes https://github.com/rust-lang/libc/issues/539

Adds many socket related constants

Started off adding a few constants to help cleaning up some `nix-rust/nix` issues.  Went a little.. further.

Adds lots of socket-related constants (`PF_*`, `MSG_*`, `AF_*`, `SO_*`, `SOL_*`, etc.) to linux/bsd flavors.

Added constants to `bsd/frebsdlike/dragonfly` for completeness, though they aren't covered by CI.  Did not touch `notbsd/linux/s390x.rs`

Add and fix tests for {i686, aarch64}-linux-android targets

I think that these changes do not breaks compatibility.

There are some types and constants changes to i686 and aarch64, but I see these changes as bug fixes instead of breaking changes. Also the type time64_t was remove from aarch64 because it is not defined in this arch.

Fixes #536

Add OXTABS and ONOEOT for BSD systems

According to all references I could find these are BSD extensions to POSIX and are also supported on OS X.

Add cfmakeraw and cfsetspeed

This includes implementations for Android. `cfsetspeed` is basically just a back-to-back call to `cfsetispeed` and `cfsetospeed`, both of which seem to do the same thing here, so I just copied that body as well for `cfsetspeed`. The implementation for `cfmakeraw` was taken from the man pages for `termios(3)`.