util: introduce compat wrappers for Winsock2

util: introduce compat wrappers for Winsock2

Windows sockets take a SOCKET HANDLE object instead of a
file descriptor. Wrap them in the same way that gnulib
does so that they use C runtime file descriptors.

While we could in theory use GSocket, it is hard to get
the exact same semantics libvirt has for its current
socket usage. Wrapping the Winsock2 APIs is thus the
easiest approach in the short term.

In changing the socke wrappers we need to re-implement
the nonblocking function too, since the GNULIB impl
expects to be used with the GNULIB sockets wrappers.

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>