socket-util: pipe for Windows.

Windows does have pipes (the interface is a little different).
We mostly use pipes in Linux to synchronize between parent and
children and also to handle fatal signals and then wake from poll_loop().

For Windows, we are using events for the same purpose. So don't
implement pipes for Windows.

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

lib/socket-util.h

@@ -65,8 +65,10 @@ int write_fully(int fd, const void *, size_t, size_t *bytes_written);
 int fsync_parent_dir(const char *file_name);
 int get_mtime(const char *file_name, struct timespec *mtime);
 
+#ifndef _WIN32
 void xpipe(int fds[2]);
 void xpipe_nonblocking(int fds[2]);
+#endif
 
 char *describe_fd(int fd);