Is your feature request related to a problem? Please describe.

Most packages use a Setup.hs which is not directly used by stack or cabal, but is used by runhaskell (as mentioned here). Ormolu always prints a warning for this file:

Found .cabal file myapp/myapp.cabal, but it did not mention myapp/Setup.hs

Describe the solution you'd like
Ormolu could recognize this as a known file when it finds a cabal file and simply attempt to format it.

Describe alternatives you've considered
I've tried marking Setup.hs as an extra source file:

extra-source-file:
    Setup.hs

but this does not squash the warning and I am not sure if this is appropriate.