…mpiler-errors

Rollup of 9 pull requests

Successful merges:

 - rust-lang#119208 (coverage: Hoist some complex code out of the main span refinement loop)
 - rust-lang#119216 (Use diagnostic namespace in stdlib)
 - rust-lang#119414 (bootstrap: Move -Clto= setting from Rustc::run to rustc_cargo)
 - rust-lang#119420 (Handle ForeignItem as TAIT scope.)
 - rust-lang#119468 (rustdoc-search: tighter encoding for f index)
 - rust-lang#119628 (remove duplicate test)
 - rust-lang#119638 (fix cyle error when suggesting to use associated function instead of constructor)
 - rust-lang#119640 (library: Fix warnings in rtstartup)
 - rust-lang#119642 (library: Fix a symlink test failing on Windows)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#119208 - Zalathar:hoist, r=WaffleLapkin,Swatinem

coverage: Hoist some complex code out of the main span refinement loop

The span refinement loop in `spans.rs` takes the spans that have been extracted from MIR, and modifies them to produce more helpful output in coverage reports.

It is also one of the most complicated pieces of code in the coverage instrumentor. It has an abundance of moving pieces that make it difficult to understand, and most attempts to modify it end up accidentally changing its behaviour in unacceptable ways.

This PR nevertheless tries to make a dent in it by hoisting two pieces of special-case logic out of the main loop, and into separate preprocessing passes. Coverage tests show that the resulting mappings are *almost* identical, with all known differences being unimportant.

This should hopefully unlock further simplifications to the refinement loop, since it now has fewer edge cases to worry about.

coverage: Replace the old span refiner with a single function

As more and more of the span refiner's functionality has been pulled out into separate early passes, it has finally reached the point where we can remove the rest of the old `SpansRefiner` code, and replace it with a single modestly-sized function.

~~There should be no change to the resulting coverage mappings, as demonstrated by the lack of changes to test output.~~

There is *almost* no change to the resulting coverage mappings. There are some minor changes to `loop` that on inspection appear to be neutral in terms of accuracy, with the old behaviour being a slightly-horrifying implementation detail of the old code, so I think they're acceptable.

Previous work in this direction includes:
- rust-lang#125921
- rust-lang#121019
- rust-lang#119208

Rollup merge of rust-lang#126294 - Zalathar:spans-refiner, r=oli-obk

coverage: Replace the old span refiner with a single function

As more and more of the span refiner's functionality has been pulled out into separate early passes, it has finally reached the point where we can remove the rest of the old `SpansRefiner` code, and replace it with a single modestly-sized function.

~~There should be no change to the resulting coverage mappings, as demonstrated by the lack of changes to test output.~~

There is *almost* no change to the resulting coverage mappings. There are some minor changes to `loop` that on inspection appear to be neutral in terms of accuracy, with the old behaviour being a slightly-horrifying implementation detail of the old code, so I think they're acceptable.

Previous work in this direction includes:
- rust-lang#125921
- rust-lang#121019
- rust-lang#119208