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`).

… ambiguity

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]

…ig-in-sugg, r=jieyouxu

Don't continue probing for method if in suggestion and autoderef hits ambiguity

The title is somewhat self-explanatory. When we hit ambiguity in method autoderef steps, we previously would continue to probe for methods if we were giving a suggestion. This seems useless, and causes an ICE when we are not able to unify the receiver later on in confirmation.

Fixes rust-lang#125432

…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

…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.*

…=workingjubilee

Simplify the `unchecked_sh[lr]` ub-checks a bit

It can use the constant in the check, rather than passing it as a parameter.

…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.