[clang] Extend -Wnonportable-include-path with a warning about trailing whitespace or dots (PR #96960)

[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 improved diagnostics.

https://github.com/llvm/llvm-project/pull/96960