Issue #14437: Fix building the _io module under Cygwin.

Misc/NEWS

@@ -78,6 +78,11 @@ Library
 - Issue #6884: Fix long-standing bugs with MANIFEST.in parsing in distutils
   on Windows.
 
+Build
+-----
+
+- Issue #14437: Fix building the _io module under Cygwin.
+
 
 What's New in Python 2.7.3 release candidate 2?
 ===============================================

Modules/_io/_iomodule.h

@@ -72,7 +72,7 @@ typedef struct {
     PyObject *filename; /* Not used, but part of the IOError object */
     Py_ssize_t written;
 } PyBlockingIOErrorObject;
-PyAPI_DATA(PyObject *) PyExc_BlockingIOError;
+extern PyObject *PyExc_BlockingIOError;
 
 /*
  * Offset type for positioning.