patch 7.4.1324
Problem:    Channels with pipes don't work on MS-Windows.
Solution:   Add pipe I/O support. (Yasuhiro Matsumoto)
diff --git a/src/structs.h b/src/structs.h
index 7f2f111..7238767 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1306,8 +1306,9 @@
 #define CHAN_SOCK   0
 #define CH_SOCK	    ch_pfd[CHAN_SOCK].ch_fd
 
-#ifdef UNIX
+#if defined(UNIX) || defined(WIN32)
 # define CHANNEL_PIPES
+# define CHAN_FD_INVALID  (-1)
 
 # define CHAN_OUT   1
 # define CHAN_ERR   2