Right now we do this to find the mongo_custom_vars.py file:

def find_mongo_custom_variables():
    files = []
    paths = [path for path in sys.path if 'site_scons' in path]
    for path in paths:
        probe = os.path.join(path, 'mongo_custom_variables.py')
        if os.path.isfile(probe):
            files.append(probe)
    return files

Which works great on POSIX platforms because SCons adds $HOME/.scons/site_scons to the sys.path. However, on Windows it does no such thing, sys.path (matching our site_scons condition) will only include the site_tools\site_scons directory.

We should inject in a path like %APPDATA%\SCons\site_scons on Windows so users on that platform can have a similar development experience as those on other systems.