Cleanup CPP in `GHC/Orphans.hs`

The CPP in `GHC/Orphans.hs` needs to be cleaned up, as it doesn't follow our best practices when it comes to CPP:

* A CPP `#if` should span the minimal range possible
* No nested CPP statements

Especially after #4527 is merged and support for GHC 9.4 series is dropped, we should revisit that module.

GHC 9.4 will likely be dropped after the next release.