Update expat to 2.2.0 to fix CVE vulnerability.

third_party/expat/files/lib/internal.h

Index: third_party/expat/files/lib/internal.h
diff --git a/third_party/expat/files/lib/internal.h b/third_party/expat/files/lib/internal.h
index dd5454831da2b4e8f3a8406a2a7c72cc79c6539e..94cb98e15cae40a81419feae3480bce4fcf3b06d 100644
--- a/third_party/expat/files/lib/internal.h
+++ b/third_party/expat/files/lib/internal.h
@@ -71,3 +71,25 @@
 #define inline
 #endif
 #endif
+
+#ifndef UNUSED_P
+# ifdef __GNUC__
+#  define UNUSED_P(p) UNUSED_ ## p __attribute__((__unused__))
+# else
+#  define UNUSED_P(p) UNUSED_ ## p
+# endif
+#endif
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+void
+align_limit_to_full_utf8_characters(const char * from, const char ** fromLimRef);
+
+
+#ifdef __cplusplus
+}
+#endif