Initial OS porting experience

[shirleyquirk]

Hacking on the compiler to enable this seems extreme to me.

> However, you'd still need to do post processing of the json file, which isn't 
> great in CMake.
    
    
    #!/usr/bin/bash
    if [ $# -ne 1 ]
    then
      echo "usage: $0 /path/to/main.json"
      exit 1
    fi
    
    jfile=$1
    changed_files=$(jq -r '.compile[] | .[0]' "$jfile")
    echo $changed_files
    
    
    Run

add a config.nims that exports `nimCacheDir() & "/" & projectName() * ".json"` 
somewhere cmake can read it pass that into cmake with `execute_process` or so