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

diff --git a/Modules/expat/internal.h b/Modules/expat/internal.h
index e33fdcb..dc4ef0c 100644
--- a/Modules/expat/internal.h
+++ b/Modules/expat/internal.h
@@ -115,6 +115,11 @@
 #endif
 
 
+#ifdef XML_ENABLE_VISIBILITY
+#if XML_ENABLE_VISIBILITY
+__attribute__ ((visibility ("default")))
+#endif
+#endif
 void
 _INTERNAL_trim_to_complete_utf8_characters(const char * from, const char ** fromLimRef);