Help user debug why `-fobject-code` or interpreted mode is turned on when using GHCi

If you use GHCi with a module which uses unboxed tuples then object code generation will be automatically turned on. This is a lot slower than the normal interpreted mode so it's helpful to structure a project so that uses of unboxed tuples are in the leaves.

It's quite easy to make a lot of modules depend on unboxed tuples by naively adding imports so there should be some way to working out how many modules will need to be compiled with -fobject-code and how to stop them from being so.

See !554 (merged)