This test fails on targets without unwinding because the proc macro was
compiled as the target, not the host. Some targets were explicitly
disabled to pass CI, but these directives are more general.

Fixes Fuchsia tests.

… Drop implementation

…mpiler-errors

Fix diagnostics for coroutines with () as input.

This may be a more real-life example to trigger the diagnostic:

```rust
#![features(try_blocks, coroutine_trait, coroutines)]

use std::ops::Coroutine;

struct Request;
struct Response;
fn get_args() -> Result<String, String> { todo!() }
fn build_request(_arg: String) -> Request { todo!() }
fn work() -> impl Coroutine<Option<Response>, Yield = Request> {
    #[coroutine]
    |_| {
        let r: Result<(), String> = try {
            let req = get_args()?;
            yield build_request(req)
        };
        if let Err(msg) = r {
            eprintln!("Error: {msg}");
        }
    }
}
```

…,fee1-dead

Fix the misleading diagnostic for `let_underscore_drop` on type without `Drop` implementation

Closes: rust-lang#130430
r? rust-lang/diagnostics

Utf8Chunks: add link to Utf8Chunk

It is currently surprisingly non-trivial to go from the `utf8_chunks` method to the docs of the `valid`/`invalid` methods used in the example. This should help.

…-errors

Fix directives for lint-non-snake-case-crate

This test fails on targets without unwinding or with `--target-rustcflags=-Cpanic=abort` because the proc macro was compiled as the target, not the host. Some targets were explicitly disabled to pass CI, but these directives are more general.

* `needs-dynamic-linking` is self explanatory
* `force-host` for proc macros
* `no-prefer-dynamic` is apparently also used for proc macros

Note that `needs-unwind` can also be useful for situations other than proc macros where unwinding is necessary.

r? ``@jieyouxu``

Update FIXME comment in s390x_unknown_linux_*.rs

- Remove comment about "LLVM < 16" since the minimum external LLVM version is 16+ since rust-lang#117947
- Reflect rename of cabi_s390x.rs in rust-lang@030244c (renamed to [abi/call/s390x.rs](rust-lang@030244c#diff-20136d4a18fa0ef9bd4fc2e6f92e88daad6be88bfb156e5702af39ee87ca4879), and it is currently [still in the same location](https://github.com/rust-lang/rust/blob/9e394f551c050ff03c6fc57f190e0761cf0be6e8/compiler/rustc_target/src/abi/call/s390x.rs)).

r? ``@cuviper``

``@rustbot`` label +O-SystemZ