Auto merge of #142791 - cuviper:beta-next, r=cuviper

[beta] backports

- Make the assertion in `Ident::new` debug-only. rust-lang/rust#140880
- Avoid creating an empty identifer in `Symbol::to_ident_string`. rust-lang/rust#141318
- Backport rust-lang/stdarch#1818 for 1.88 rust-lang/rust#142694
- [beta] Clippy backport rust-lang/rust#142725
    - ICE:
        - https://github.com/rust-lang/rust-clippy/pull/14776
    - Lint contradictions:
        - https://github.com/rust-lang/rust-clippy/pull/14703
        - https://github.com/rust-lang/rust-clippy/pull/14810
    - Smaller (in LoC changes) fixes:
        - https://github.com/rust-lang/rust-clippy/pull/14733
        - https://github.com/rust-lang/rust-clippy/pull/14730
-  [win][ci] Update LLVM toolchain used to build LLVM to 20 rust-lang/rust#140757

r? cuviper