Platform shims for Windows (#6548)

* Platform shims for Windows

* Satisfy linter

src/shims/windows/sys/socket.h

@@ -0,0 +1,46 @@
+#ifndef SOCKET_H
+#define SOCKET_H
+
+typedef unsigned short sa_family_t;
+
+#include <Winsock2.h>
+#include <unistd.h>  // ssize_t
+
+#define cmsghdr _WSACMSGHDR
+#undef CMSG_DATA
+#define CMSG_DATA WSA_CMSG_DATA
+#define CMSG_SPACE WSA_CMSG_SPACE
+#define CMSG_FIRSTHDR WSA_CMSG_FIRSTHDR
+#define CMSG_LEN WSA_CMSG_LEN
+#define CMSG_NXTHDR WSA_CMSG_NXTHDR
+
+#define SCM_RIGHTS 1
+
+#define iovec _WSABUF
+#define iov_base buf
+#define iov_len len
+#define msghdr _WSAMSG
+#define msg_name name
+#define msg_namelen namelen
+#define msg_iov lpBuffers
+#define msg_iovlen dwBufferCount
+#define msg_control Control.buf
+#define msg_controllen Control.len
+#define msg_flags dwFlags
+
+int dumb_socketpair(SOCKET socks[2]);
+ssize_t sendmsg(int sockfd, struct msghdr *msg, int flags);
+ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags);
+int socketpair(int domain, int type, int protocol, int sv[2]);
+
+#ifdef __cplusplus
+namespace {
+inline int send(SOCKET s, const void *buf, int len, int flags) {
+  // Call the const char* overload version
+  int (*psend)(SOCKET s, const char *buf, int len, int flags) = ::send;
+  return (*psend)(s, (const char *)buf, len, flags);
+}
+}  // namespace
+#endif
+
+#endif /* SOCKET_H */