[clang] [Clang] Add warning for non-portable include paths with trailing whitespace or dots (PR #190610)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

Thank you for the patch.

Note the [How to Submit a Patch](https://llvm.org/docs/Contributing.html#how-to-submit-a-patch) section of `Contributing to LLVM` document states "not contain any unrelated changes". Right now your changes to `PPDirectives.cpp` contain mostly unrelated changes. Please revert any changes not directly related to the issue you are fixing. Please make sure you are familiar with the guidelines and [LLVM Coding Standards](https://llvm.org/docs/CodingStandards.html). If you have questions you can asking in the `#clang` channel in llvm discord.

Please also make sure you are using `.clang-format` from the llvm project and not some other local format config.

https://github.com/llvm/llvm-project/pull/190610