Added missing includes to avoid warnings/errors.

diff --git a/server/pipe.c b/server/pipe.c
index 1f92d10..06260f9 100644
--- a/server/pipe.c
+++ b/server/pipe.c
@@ -17,7 +17,7 @@
 #include <unistd.h>
 
 #include "winerror.h"
-#include "winnt.h"
+#include "winbase.h"
 #include "server/thread.h"
 
 enum side { READ_SIDE, WRITE_SIDE };