[llvm] Add a script to check for and fix trailing whitespace (PR #123496)

[via llvm-commits]

cor3ntin wrote:

> Currently this is a draft - there are several occurrences of intentional trailing whitespace and I am not sure how best to accommodate these. Probably looking for something like ALLOW TRAILING WHITESPACE in a comment. I also need to test the diff parsing more.

The clang formatting check/bot does not prevent approving/merging a PR - Presumably the intent is the same here? 

https://github.com/llvm/llvm-project/pull/123496