Relative paths in cabal.project files don't work as expected

I want to pass some options to a dependency. So I added the flags to my cabal.project file as follows.

```
package groups
ghc-options: -fwrite-ide-info -hiedir=./test/hie-files
```

However, now `groups` is rebuilt but the `hie` files are not in the directory I specified and nor are they anywhere to be seen at all! I can't find them anywhere in my home directory.

If I write an absolute path it works fine.

Why I consider this a bug, if I `cabal get groups`, modify the cabal file to add the ghc-options and add it as a local dependency then the path is resolved relative to the cabal file.

Start with the cabal.project package stanza containing ghc-options and compare how relative paths are handled for a local dependency versus the external groups dependency obtained with cabal get. Reproduce the -hiedir behavior, then confirm that the generated HIE files appear in the documented relative location without requiring an absolute path.

Written by the indexing model from the issue text.