Two improvements to the documentation:
- Document `-` as a valid character for signed integer destinations
- Make the documentation even more clear that extra whitespace and non-digit characters is invalid. Many other
  languages, e.g. c++, are very permissive in string to integer routines and simply try to consume as much as they can,
  ignoring the rest. This is trying to make the transition for developers who are used to the conversion semantics in
  these languages a bit easier.

…of path

…f paths

…stead of paths

…ead of path

…ostic items instead of paths

…ad of path

… of paths

…f path

… path

…f path

…m instead of path

…tead of path

…f paths

Improve documentation for <integer>::from_str_radix

Two improvements to the documentation:
- Document `-` as a valid character for signed integer destinations
- Make the documentation even more clear that extra whitespace and non-digit characters is invalid. Many other languages, e.g. c++, are very permissive in string to integer routines and simply try to consume as much as they can, ignoring the rest. This is trying to make the transition for developers who are used to the conversion semantics in these languages a bit easier.

…ompiler-errors

[Clippy] Get rid of most `std` `match_def_path` usage, swap to diagnostic items.

Part of rust-lang/rust-clippy#5393.

This was going to remove all `std` paths, but `SeekFrom` has issues being cleanly replaced with a diagnostic item as the paths are for variants, which currently cannot be diagnostic items.

This also, as a last step, categories the paths to help with future path removals.

…atrieb

`pal::unsupported::process::ExitCode`: use an `u8` instead of a `bool`

`ExitCode` should “represents the status code the current process can return to its parent under normal termination”, but is currently represented as a `bool` on unsupported platforms, making the `impl From<u8> for ExitCode` lossy.

Fixes rust-lang#130532.

History: [IRLO thread](https://internals.rust-lang.org/t/mini-pre-rfc-redesigning-process-exitstatus/5426) (`ExitCode` as a `main` return), rust-lang#48618 (initial impl), rust-lang#93445 (`From<u8>` impl).

Mark the `link_cfg` feature as internal

This PR marks the `link_cfg` feature as internal because it's a perme-unstable feature, only used by `core`/`std`and `unwind`.

Support 128-bit atomics on s390x

Since LLVM 18 (llvm/llvm-project@c568927), 128-bit atomics are fully supported on s390x. And the current minimum external LLVM version is now 18 (rust-lang#130487).

s390x 128-bit atomic instructions (lpq,stpq,cdsg) has been present since [the First Edition of the Principles of Operation](https://publibfp.dhe.ibm.com/epubs/pdf/dz9zr000.pdf). (LLVM's minimal supported architecture level [is z10 (the Eighth Edition of the PoP)](https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/SystemZ/SystemZProcessors.td#L16-L17).)

cc rust-lang#99069

r? `@cuviper`