Fixes rust-lang#128690

The two altered expectation messages both seem like improvements:

- `coerce-expect-unsized-ascribed.stderr` says you can go
  `Box<char> -> Box<dyn Debug>`, which you can.
- `upcast_soundness_bug.stderr` used to say that you could go
  `Box<dyn Trait<u8, u8>> -> Box<dyn Trait>`, which you can't,
  because the type parameters are missing in the destination
  and the only ones that work aren't what's needed.

…t method

This makes more things match, particularly applicable blankets.

…youxu

Migrate `remap-path-prefix-dwarf` `run-make` test to rmake

Part of rust-lang#121876 and the associated [Google Summer of Code project](https://blog.rust-lang.org/2024/05/01/gsoc-2024-selected-projects.html).

Possibly my proudest branch name yet.

try-job: aarch64-apple
try-job: armhf-gnu
try-job: test-various
try-job: x86_64-gnu-llvm-18

…, r=workingjubilee,compiler-errors

alloc: add ToString specialization for `&&str`

Fixes rust-lang#128690

…k-Simulacrum

Add windows-targets crate to std's sysroot

With this PR, when backtrace is used as a crate from crates.io it will (once updated) use the real [windows-targets](https://crates.io/crates/windows-targets) crate. But when used from std it'll use std's replacement version.

This allows sharing our customized `windows_tagets::link!` macro between std proper and the backtrace crate when used as part of std, ensuring a consistent linking story. This will be especially important once we move to using [`raw-dylib`](https://doc.rust-lang.org/reference/items/external-blocks.html#dylib-versus-raw-dylib) by default.

chore(lib): Enhance documentation for core::fmt::Formatter's write_fm…

fix: rust-lang#128713

Use `is_lang_item` more

Few places that I missed since introducing `TyCtxt::is_lang_item`.

…rrors

Remove a no-longer-true assert

Fixes rust-lang#129009

The assert was simply no longer true. I thought my test suite was thorough but I had not noticed these `let`-specific diagnostics codepaths.

r? `@compiler-errors`