Report the original XML parse error

Don't hide the XML error with an
unrelated exception (wrong number of arguments
to sys.stderr.write) but reraise it.

tools/build/make_cross_refs.py

@@ -255,7 +255,8 @@ def main():
         try:
             et = ET.parse(f)
         except ET.ParseError:
-            sys.stderr.write("ERROR parsing", f, "\n")
+            print("ERROR parsing", f, file=sys.stderr)
+            raise
         fname = os.path.basename(f)
         if fname.startswith("namespaceIMP"):
             if verbose: