Dynamic object files are nearly always built

It's very hard to stop dynamic object files being built.

1. Documentation states that `shared: False` and `dynamic-executable: False`, so you would expect dynamic interface files to not be built by default.
2. If you set either of these options, shared libraries are still built because `ghci` needs shared libraries. See `compilerShouldUseSharedLibsByDefault`.
3. Even if you set `shared: False` explicitly, shared libraries are built because of the use of `liftA2` in `pkgsUseSharedLibrary` requires that **both** `shared:False` and `dynamic-executable: False` is set.

If you set both these options then cabal only produces .hi files.

However, if you then using `cabal repl` fails because dynamic object files are not forced to be built when we are using ghci.

I just write this down as it's pretty confusing what is going on.