Update constants header generator.

Author: aardvark179

tool/generate-cext-constants.rb

@@ -142,7 +142,7 @@
   constants.each do |macro_name, name, _|
     f.puts
     f.puts "VALUE rb_tr_get_#{name}(void) {"
-    f.puts "  return (VALUE) polyglot_invoke(RUBY_CEXT, \"#{macro_name}\");"
+    f.puts "  return RUBY_CEXT_INVOKE(\"#{macro_name}\");"
     f.puts "}"
   end
 end