Excise DL_EXPORT from Include.

Thanks to Skip Montanaro and Kalle Svensson for the patches.
diff --git a/Include/boolobject.h b/Include/boolobject.h
index 0259126..e7a4e60 100644
--- a/Include/boolobject.h
+++ b/Include/boolobject.h
@@ -9,7 +9,7 @@
 
 typedef PyIntObject PyBoolObject;
 
-extern DL_IMPORT(PyTypeObject) PyBool_Type;
+PyAPI_DATA(PyTypeObject) PyBool_Type;
 
 #define PyBool_Check(x) ((x)->ob_type == &PyBool_Type)
 
@@ -17,14 +17,14 @@
 Don't forget to apply Py_INCREF() when returning either!!! */
 
 /* Don't use these directly */
-extern DL_IMPORT(PyIntObject) _Py_ZeroStruct, _Py_TrueStruct;
+PyAPI_DATA(PyIntObject) _Py_ZeroStruct, _Py_TrueStruct;
 
 /* Use these macros */
 #define Py_False ((PyObject *) &_Py_ZeroStruct)
 #define Py_True ((PyObject *) &_Py_TrueStruct)
 
 /* Function to return a bool from a C long */
-extern DL_IMPORT(PyObject *) PyBool_FromLong(long);
+PyAPI_FUNC(PyObject *) PyBool_FromLong(long);
 
 #ifdef __cplusplus
 }