musl: fix linkage of libc

I messed up the logic of the cfg during my rebase of #163 

musl: add support for mips/mipsel

Definitions for i686-unknown-linux-musl, arm and asmjs musl

I've tested x86 against C locally, but not arm or asmjs.
I added the arm definitions because asmjs's C is derived from arms.

Mysteriously, my locally-built musl does not contain a
definition for _SC_2_C_VERSION, so I just removed it.

stdbuild conditional change

Building with cargo doesn't necessarily imply this isn't a `stdbuild` libc. This logic is more consistent with the rest of the repo.

Renames "sunos" to "solaris" (as a part of PR to add Illumos support to Rust)

Add pthread_setname_np for NetBSD

Fixes #156

Bump to 0.2.6

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.