Implement socketpair(domain, type, protocol, fds[]) in POSIX and LibC.
* Implement sendmsg(socket, msg, flags) and recvmsg(socket, msg, flags).
* Add allocateMsgHdr() to POSIX to allocate structures.
* Implement layout for MacOS only thus far. (All others throw not-implemented).
Remove JDK7ism of StandardCharset.
Remove unused import of StandardCharsets (Java 7+).
Do not ignore test failures.
Add Linux64 support for sendmsg()/recvmsg().