Conditional data-files

**What is your question?**
I need to install different `data-files` depending on a condition (in my case which compiler it is).
I tried using an `if`, but that doesn't seem to work.

Is there no way to do this? Or am I just being stupid?

**System information**
cabal-install version 3.12.1.0
compiled using version 3.12.1.0 of the Cabal library

Start by reproducing the conditional data-files configuration described in the issue with cabal-install 3.12.1.0 and the Cabal library version listed. Read the existing Cabal package-configuration documentation and behavior around conditional fields. Done means establishing whether compiler-dependent data-files are supported and, if not, defining the required change clearly.

Written by the indexing model from the issue text.