This PR removes the static check that disallowed extern functions
with ellipsis (varargs) as the only parameter since this is now
valid in C23.

Also, adds a doc comment for `check_decl_cvariadic_pos()` and
fixes the name of the function (`varadic` -> `variadic`).

Otherwise, it's unclear when the nomination label is removed whether the
backport was accepted, thus nomination removed, or if the backport was
rejected, thus nomination removed.

…variadics, r=compiler-errors

Support C23's Variadics Without a Named Parameter

Fixes rust-lang#123773

This PR removes the static check that disallowed extern functions
with ellipsis (varargs) as the only parameter since this is now
valid in C23.

This will not break any existing code as mentioned in the proposal
document: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2975.pdf.

Also, adds a doc comment for `check_decl_cvariadic_pos()` and
fixes the name of the function (`varadic` -> `variadic`).

…r=cjgillot

Only allow immutable statics with #[linkage]

…nst-body, r=cjgillot

Don't skip out of inner const when looking for body for suggestion

Self-explanatory title, I'll point out the important logic in an inline comment.

Fixes rust-lang#125370

cleanup dependence of `ExtCtxt` in transcribe when macro expansion

part of rust-lang#125356
We can remove `transcribe`’s dependence on `ExtCtxt` to facilitate subsequent work (such as moving macro expansion into the incremental compilation system)

r? ``@petrochenkov``
Thanks for the reviewing!

crashes: increment the number of tracked ones

r? ```@jieyouxu```

…ific, r=jieyouxu

Also mention my-self for other check-cfg docs changes

This PR adds a mention for my-self for the recently added `src/doc/rustc/src/check-cfg` directory.

*I had to add a second mention just for the directory since [`Path::starts_with`](https://doc.rust-lang.org/std/path/struct.Path.html#method.starts_with) as used by [triagebot](https://github.com/rust-lang/triagebot/blob/48f29f351cae774caa90f555fbbc6d0df7dce80e/src/handlers/mentions.rs#L69), matches on path components and so can never return true for a file and directory at the same time.*

…meGomez

Notify T-rustdoc for beta-accepted and stable-accepted too

Otherwise, it's unclear when the nomination label is removed whether the backport was accepted, thus nomination removed, or if the backport was rejected, thus nomination removed.

r? ```@GuillaumeGomez```

Avoid a `FieldIdx::from_usize` in InstSimplify

Just a tiny cleanup I noticed in passing while looking at something unrelated.