[clang] [Clang](NFC) Add coverage for VTable debug info (PR #151818)

[Javier Lopez-Gomez via cfe-commits]

https://github.com/jalopezg-git commented:

Thank you!  I have added some minor comments / suggestions that add to other reviewer's comments :slightly_smiling_face:.

https://github.com/llvm/llvm-project/pull/151818