I'll answer my own question in case this topic interests anyone else.
Microsoft Visual Studio Community Edition is free as is Arduino IDE for Visual Studio (http://www.visualmicro.com/).
You can open Marlin.ico in Visual Studio and the builtin editor uses color coding to indicate which #defines are active and therefore which code is actually going to be compiled.
Microsoft Visual Studio Community Edition is free as is Arduino IDE for Visual Studio (http://www.visualmicro.com/).
You can open Marlin.ico in Visual Studio and the builtin editor uses color coding to indicate which #defines are active and therefore which code is actually going to be compiled.