send, sendto, sendmsg, recv, recvfrom and recvmsg failed with EOPNOTSUPP for
MSG_DONTWAIT on Windows, where FreeBSD 11.4 sosend_generic and
soreceive_generic make the one call non-blocking and fail with EWOULDBLOCK
when it would wait. Winsock has no per-call flag, so the call now asks WSAPoll
with a zero timeout whether the socket is ready and fails with EAGAIN when it
is not. The Windows branches of the socket tests that expected EOPNOTSUPP now
run the same checks as the other hosts.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>