patch 8.2.4316: __CYGWIN32__ is not defined on 64 bit systems

Problem:    __CYGWIN32__ is not defined on 64 bit systems.
Solution:   Update #ifdefs. (Ken Takata, closes #9709)
diff --git a/src/vim.h b/src/vim.h
index 86acb6d..33d294c 100644
--- a/src/vim.h
+++ b/src/vim.h
@@ -1576,10 +1576,10 @@
 #endif
 
 /*
- * EMX doesn't have a global way of making open() use binary I/O.
+ * Cygwin doesn't have a global way of making open() use binary I/O.
  * Use O_BINARY for all open() calls.
  */
-#if defined(__CYGWIN32__)
+#ifdef __CYGWIN__
 # define O_EXTRA    O_BINARY
 #else
 # define O_EXTRA    0