Make value of Cabal flags accessible through an autogenerated Haskell module

Say, I have `mypkg.cabal` containing:
~~~~
Flag special
Description: Extra feature for you
~~~~

It would nice if Cabal would create a file, say `Flag_mypkg.hs`, that I can use like so:
~~~~
import qualified Flag_mypkg

main :: IO ()
main =
if Flag_mypkg.special
then putStrLn "special"
else putStrLn "normal"
~~~~