What's the midl option for disabling preprocessor? I couldn't find it.
It's `-nocpp`.
Note that this change can potentially break working reasonable scenarios, like importing SDK IDLs in a IDL file that doesn't use preprocessor and then building it with -N. It's probably not a big deal as I don't expect -N to be popular, but if using the helper in main is the only reason for the change, I'd suggest to handle no_preprocess in main instead. You may still use the helper for the rest of the job.
Sure, makes sense.