A picture is worth a thousand words, they say.
Naggy is an AVR Studio 5 extension I wrote that uses Clang to show compiler diagnostics as you type. You can download it from here and the source is available here. Just double click on the downloaded VSIX and you should be good to go.
As its version number (0.1) indicates, it is still a very raw product (see issues). In case you run into problems, you can always do Tools –> Extension Manager –> Naggy –> Disable (or Uninstall).