For ghc calls pass Cabal's build/ directory after user's src/ directory so...

For ghc calls pass Cabal's build/ directory after user's src/ directory so that contents of src/ takes precedence (#8690)

* Add test

* Pass build/ directory after src/ so that whatever’s in src/ will override any files we autogenerated

* Add expected output. Constrait test to run on recent enough ghc that will have Cabal updated

* Force test to requre development version of Cabal

Otherwise output will not be correct. It’s tricky to pass proper
Cabal/ version to this test because it needs it for the custom setup.

* Add changelog

* Fix other tests