patch 8.0.1030: MS-Windows: wrong size computation in is_cygpty()

Problem:    MS-Windows: wrong size computation in is_cygpty().
Solution:   Compute the size properly. (Ken Takata)
diff --git a/src/iscygpty.h b/src/iscygpty.h
index fbca4b4..82fd0af 100644
--- a/src/iscygpty.h
+++ b/src/iscygpty.h
@@ -2,7 +2,7 @@
  * iscygpty.h -- part of ptycheck
  * https://github.com/k-takata/ptycheck
  *
- * Copyright (c) 2015-2016 K.Takata
+ * Copyright (c) 2015-2017 K.Takata
  *
  * You can redistribute it and/or modify it under the terms of either
  * the MIT license (as described below) or the Vim license.
@@ -30,7 +30,12 @@
 #ifndef _ISCYGPTY_H
 #define _ISCYGPTY_H
 
+#ifdef _WIN32
 int is_cygpty(int fd);
 int is_cygpty_used(void);
+#else
+#define is_cygpty(fd)		0
+#define is_cygpty_used()	0
+#endif
 
 #endif /* _ISCYGPTY_H */