Should warn about overlapping "hs-source-dirs"

The logic should be that if a package component declares a dependency on a library or sub-library in the package, then `hs-source-dirs` should not overlap. This is because imports that occur within the executable / test-suite / benchmark / sub-library etc will instead recompile the code, which is a waste.

It also potentially has other negative effects - https://github.com/commercialhaskell/stack/issues/3109#issuecomment-343911878