…RalfJung

Avoid various uses of `Option<Span>` in favor of using `DUMMY_SP` in the few cases that used `None`

based on rust-lang#122471

`DUMMY_SP` is already the sentinel value we have that says "no span". We don't need to wrap these `Span`s in a separate `Option`.

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#122480 (Avoid various uses of `Option<Span>` in favor of using `DUMMY_SP` in the few cases that used `None`)
 - rust-lang#122567 (Remove fixme about LLVM basic block naming)
 - rust-lang#122588 (less useless filter calls in imported_source_file)
 - rust-lang#122647 (add_retag: ensure box-to-raw-ptr casts are preserved for Miri)
 - rust-lang#122649 (Update the minimum external LLVM to 17)
 - rust-lang#122680 (Do not eat nested expressions' results in `MayContainYieldPoint` format args visitor)
 - rust-lang#122683 (add missing test: expected paren or brace in macro)
 - rust-lang#122689 (Add missing `try_visit` calls in visitors.)

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

Rollup merge of rust-lang#122480 - oli-obk:const-eval-span-no-opt, r=RalfJung

Avoid various uses of `Option<Span>` in favor of using `DUMMY_SP` in the few cases that used `None`

based on rust-lang#122471

`DUMMY_SP` is already the sentinel value we have that says "no span". We don't need to wrap these `Span`s in a separate `Option`.

Upgrades the Rust toolchain to `nightly-2024-03-21`. The relevant
changes in Rust are:
* rust-lang/rust#122480
* rust-lang/rust#122748
* rust-lang/cargo#12783

I wasn't confident that our regression testing could detect differences
in the file paths being generated with the new logic, so I added code
similar to the following just to check they were equivalent:
```rust
             let base_filename = tcx.output_filenames(()).output_path(OutputType::Object);
+            let binding = tcx.output_filenames(()).path(OutputType::Object);
+            let base_filename2 = binding.as_path();
+            assert_eq!(base_filename, base_filename2);
```
Note that this was done for each instance where we used `output_path`,
and completed regression testing with the previous toolchain version. I
also checked manually the instance where we generate a `.dot` graph for
debug purposes following the instructions
[here](https://model-checking.github.io/kani/cheat-sheets.html?highlight=dot#debug)
(a `libmain.dot` file was generated for the `main.rs` in one of my
projects).

---------

Co-authored-by: Celina G. Val <[email protected]>

…rrors

replace another Option<Span> by DUMMY_SP

This was missed in rust-lang#122480.

Rollup merge of rust-lang#124842 - RalfJung:option-span, r=compiler-errors

replace another Option<Span> by DUMMY_SP

This was missed in rust-lang#122480.