bpo-31374: expat doesn't include <pyconfig.h> on Windows (GH-11079)

diff --git a/Modules/expat/xmltok.c b/Modules/expat/xmltok.c
index fa35de7..6371a35 100644
--- a/Modules/expat/xmltok.c
+++ b/Modules/expat/xmltok.c
@@ -30,7 +30,9 @@
    USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
-#include <pyconfig.h>
+#if !defined(_WIN32) && defined(HAVE_EXPAT_CONFIG_H)
+#  include <pyconfig.h>
+#endif
 #include <stddef.h>
 #include <string.h>  /* memcpy */