Add IP v6 group membership options to OpenBSD build

Add IPV6_JOIN_GROUP and IPV6_LEAVE_GROUP sockopt constants.

unix: Add if_indextoname and IF_NAMESIZE

Add SOCK_NONBLOCK & SOCK_CLOEXEC

Linkify more docs, add more tested triples

Now we're testing rumprun, openbsd, and freebsd

Bump to 0.2.5

Fixes #144 by defining O_ACCMODE for BSD's

Preliminary PowerPC Support

Add IP_TRANSPARENT socket option

Required for transparent proxying

FreeBSD and OpenBSD CI

* The `flock` structure has an extra field
* Some `flock`-related constants have different value
* Some constants like `TABN` don't exist
* The `fsblkcnt_t` and `fsfilcnt_t` type definitions are u64 for x86_64 FreeBSD
* The `d_namelen` field in `dirent` was renamed correctly to `d_namlen`
* The alignment of `fd_set` was off, and the macros were updated to not always
  assume a 32-bit integer is used.

This commit adds support to test all libc definitions on both OpenBSD and
FreeBSD via QEMU userspace emulation. Specially prepared images for each OS are
used which are essentially intended to run a script on startup and then exit.
Documentation has been added to the `ci/README.md` file describing this new
system.

Add Illumos support

Add setns api to linux targets

Adds setns libc api to all linux targets

Signed-off-by: Jana Radhakrishnan <mrjana@gmail.com>

Add powerpc64 and powerpc64le support

A number of libc constants are different on PowerPC64 Linux, so push
them down into arch specific files.

Skip C/Rust type checks for eventfd.

Correct MIPS types of SA_* flags

Missed out correction from 6ac75c16

libc-test's C program should not #include <linux/fs.h> on Linux

Adjust MIPS MS_RMT_MASK to match <sys/mount.h>.