Auto merge of #116316 - cjgillot:incr-privacy, r=petrochenkov

Remove eval_always from check_private_in_public.

This PR attempts to avoid re-computing `check_private_in_public` query. First by marking the query as non-`eval_always`, and by reducing the amount of accesses to HIR as much as possible.

Latest perf rust-lang/rust#116316 (comment) shows that we manage it. The cost is extra dep-graph bookkeeping.

Author: bors