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/vim.h b/src/vim.h
index 0297cfd..52eebab 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1730,7 +1730,7 @@
 typedef int proftime_T;	    /* dummy for function prototypes */
 #endif
 
-#ifdef WIN64
+#ifdef _WIN64
 typedef __int64 sock_T;
 #else
 typedef int sock_T;