A way to specify options to local packages only.

Say I develop `Cabal`

```
package Cabal
flags: foo
```

will also affect qualified packages (`setup-depends`), which is something I don't want to affect, as that causes dependency rebuilds.

No files or tests are named. Start by reading how Cabal applies flags from a package stanza to setup-depends packages, then determine where local-package-only scope could be represented. Done means options for the local Cabal package no longer affect qualified packages or trigger their dependency rebuilds.

Written by the indexing model from the issue text.