Unused modules incorrectly flagged on re-exports

Describe the bug If you add build-depends on a library that only contains re-exports, the -Wunused-packages warning triggers.

To Reproduce

1. Define a module in an internal library component
2. Re-export the module in the library component.
3. Add the library component to a build-depends of an executable component.
4. Use the module from an executable component.
5. Enable -Wunused-packages and -Werror on the executable component.
6. Build the project.

The build fails.

Expected behavior The build should succeed.

System information cabal-3.4.0.0, ghc-8.10.4

Additional context N/A

Originally reported here: https://github.com/haskell/cabal/issues/7357

See the original ticket for example.