incr.comp.: Make sure dependencies are recorded when feeding queries during eval-always queries.
This PR makes sure we don't drop dependency edges when feeding queries during an eval-always query.
Background: During eval-always queries, no dependencies are recorded because the system knows to unconditionally re-evaluate them regardless of any actual dependencies. This works fine for these queries themselves but leads to a problem when feeding other queries: When queries are fed, we set up their dependency edges by copying the current set of dependencies of the feeding query. But because this set is empty for eval-always queries, we record no edges at all -- which has the effect that the fed query instances always look "green" to the system, although they should always be "red".
The fix is to explicitly add a dependency on the artificial "always red" dep-node when feeding during eval-always queries.
Fixes https://github.com/rust-lang/rust/issues/108481
Maybe also fixes issue https://github.com/rust-lang/rust/issues/88488.
cc `@jyn514`
r? `@cjgillot` or `@oli-obk`
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