Support Cabal HEAD in "stack ghci"

From https://github.com/haskell/cabal/blob/master/Cabal/changelog

> 1.25.x.x (current development version)
> - Backwards incompatible change to 'cabal_macros.h' (#1893): we now
> generate a macro file for each component which contains only
> information about the direct dependencies of that component.
> Consequently, 'dist/build/autogen/cabal_macros.h' contains
> only the macros for the library, and is not generated if a
> package has no library; to find the macros for an executable
> named 'foobar', look in 'dist/build/foobar/autogen/cabal_macros.h'.

`stack ghci` will need to change its `cabal_macros.h` processing conditionally based on Cabal version.