Allow to use Actions in config file environment

[kaoskorobase]

Allow to use actions in config file environment, i.e. change withConfig signature to

withConfig :: [FilePath]
           -> Rules (   [(String, Action String)]
                     -> FilePath
                     -> String
                     -> Action (Maybe String))

Use case: Pass toolchain variant determined from host toolchain (returned in Action monad) to config file environment.