add additional import alias for newer GHC versions

[joel-bach]

Fix for https://github.com/Haskell-OpenAPI-Code-Generator/Haskell-OpenAPI-Client-Code-Generator/issues/123

[schoettl]

The generated modules now make GHC.Internal.* available via aliases. So that the rest of the generated code can access GHC.Internal.*?

Just out of curiosity, why is this the preferred solution? Wouldn't another solution be to not access the GHC internal namespace at all and use Data.Maybe etc. instead?

[joel-bach]

@schoettl We use template-haskell for the code generation and it seems like even if you do not access internal modules during the generation, they can still get exposed in the actually generated code. I assume this is due to the fact that template-haskell is not designed for code generation written to file but instead for ad-hoc generation during compilation where these quirks are internals of the compiler.

[schoettl]

Ah, makes sense. Thanks!