[2.7] bpo-31374: Include pyconfig.h earlier in expat (GH-11078)

Include <pyconfig.h> ealier in Modules/expat/xmlparse.c to define
properly _POSIX_C_SOURCE and _XOPEN_SOURCE.

Modules/expat/xmlparse.c

@@ -30,6 +30,9 @@
    USE OR OTHER DEALINGS IN THE SOFTWARE.
 */
 
+#if !defined(_WIN32) && defined(HAVE_EXPAT_CONFIG_H)
+#  include <pyconfig.h>
+#endif
 #if !defined(_GNU_SOURCE)
 # define _GNU_SOURCE 1                  /* syscall prototype */
 #endif

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 */