Fix breakage from patch 1471883 (r45800 & r45808) on OSF/1.
The problem was that pyconfig.h was being included before some system headers
which caused redefinitions and other breakage.  This moves system headers
after expat_config.h which includes pyconfig.h.
diff --git a/Modules/expat/xmlparse.c b/Modules/expat/xmlparse.c
index 3372bc9..42d95b7 100644
--- a/Modules/expat/xmlparse.c
+++ b/Modules/expat/xmlparse.c
@@ -2,10 +2,6 @@
    See the file COPYING for copying permission.
 */
 
-#include <stddef.h>
-#include <string.h>                     /* memset(), memcpy() */
-#include <assert.h>
-
 #define XML_BUILDING_EXPAT 1
 
 #ifdef COMPILED_FROM_DSP
@@ -16,6 +12,10 @@
 #include <expat_config.h>
 #endif /* ndef COMPILED_FROM_DSP */
 
+#include <stddef.h>
+#include <string.h>                     /* memset(), memcpy() */
+#include <assert.h>
+
 #include "expat.h"
 
 #ifdef XML_UNICODE