…rtdev

Add CFI tests for return types and never type

In a few different conversations, the CFI types of various functions has come up. First, the CFI type of returning `!` came up in rust-lang#159446 (comment), where we found that it doesn't have the same CFI type as returning `()`, which it probably should.

Then in rust-lang#159935, I wanted to make sure that this does not change the CFI type of functions when `*mut c_void` appears as an argument. Luckily it does not since it's a lang item, but there's no test for this case.

Thus, add tests for all of these cases and a few others.

AI assistance was involved with writing the test.

…uwer

Rollup of 28 pull requests

Successful merges:

 - #159638 (bootstrap: Split the `Step` trait into multiple traits)
 - #159774 (rustc_trait_selection: fix trait solver hang caused by degenerate obligations)
 - #159837 (line-tables-only test: check that the line number matches the function name)
 - #159946 (Update Enzyme submodule to imporve llvm-cov)
 - #159962 (miri subtree update)
 - #156570 (tests: extend remap-path-prefix-std to all stdlib rlibs)
 - #159617 (Fix up `#[linkage]` target checking)
 - #159633 (Improve workings of attribute suggestions)
 - #159733 (std: Switch implementations of `thread_local!` for WASI)
 - #159783 (Check unsafe impls on safe EIIs)
 - #159810 (Add tuple never coercion collection regression test)
 - #159826 (Remove redundant `#[rustc_paren_sugar]` feature gate)
 - #159846 (Implement `str::copy_from_str`)
 - #159849 (rustc_parse: Stop returning `Option` from statement parsing)
 - #159853 (Updated expect messages for `CString` struct and method documentation)
 - #159875 (More cleanup in `rustc_attr_parsing`)
 - #159882 (Update expect messages in library/alloc/boxed.rs and library/alloc/string.rs to follow the style guide)
 - #159891 (Split multiline derives into std/rustc macros)
 - #159893 (Fix `find_attr` hygiene and `rustc_hir` cleanups)
 - #159895 (rustc-dev-guide subtree update)
 - #159902 (Clarify that the expected runtime symbols signature is for the current target only)
 - #159914 (Fix error in diagnostic on_unmatched_args)
 - #159917 (spare capacity mut constification)
 - #159918 (rename abort_unwind → abort_on_unwind)
 - #159927 (Remove sve2 from the ImpliedFeatures of AArch64 v9a.)
 - #159936 (Minor `rustc_ast::ast` doc cleanups)
 - #159945 (Update expect messages in library/core/src/ptr/non_null.rs)
 - #159950 (Add CFI tests for return types and never type)