closes bpo-37437: Update vendorized expat to 2.2.7. (GH-14436)

diff --git a/Modules/expat/expat_external.h b/Modules/expat/expat_external.h
index 2d96b4f..875225d 100644
--- a/Modules/expat/expat_external.h
+++ b/Modules/expat/expat_external.h
@@ -35,10 +35,6 @@
 
 /* External API definitions */
 
-/* Namespace external symbols to allow multiple libexpat version to
-   co-exist. */
-#include "pyexpatns.h"
-
 #if defined(_MSC_EXTENSIONS) && !defined(__BEOS__) && !defined(__CYGWIN__)
 # define XML_USE_MSC_EXTENSIONS 1
 #endif
@@ -97,7 +93,11 @@
 # endif
 #endif  /* not defined XML_STATIC */
 
-#if !defined(XMLIMPORT) && defined(__GNUC__) && (__GNUC__ >= 4)
+#ifndef XML_ENABLE_VISIBILITY
+# define XML_ENABLE_VISIBILITY 0
+#endif
+
+#if !defined(XMLIMPORT) && XML_ENABLE_VISIBILITY
 # define XMLIMPORT __attribute__ ((visibility ("default")))
 #endif