[clang] [Clang] Implement diagnostics for why is_empty is false (PR #145044)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for working on this! Please be sure to add a release note to `clang/docs/ReleaseNotes.rst` so users know about the improvement.

https://github.com/llvm/llvm-project/pull/145044