Add getaddrinfo and freeaddrinfo

[andrewthad]

The will be needed to get hostname resolution working in the sockets library. These functions call further into question the current way that struct sockaddr is handled in posix-api. Consider that struct addrinfo is defined as:

struct addrinfo {
    int              ai_flags;
    int              ai_family;
    int              ai_socktype;
    int              ai_protocol;
    socklen_t        ai_addrlen;
    struct sockaddr *ai_addr;
    char            *ai_canonname;
    struct addrinfo *ai_next;
};

The current SocketAddress approach does not work at all with the sockaddr-in-a-struct that we see here and in things like recvmmsg.