[clang] [Clang] Implement C++26 P2748R5 "Disallow Binding a Returned Glvalue to a Temporary" (PR #89942)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.

1 Nit, else LGTM, the CWG issue change seems sensible, as does the rest.

https://github.com/llvm/llvm-project/pull/89942