[clang] Fix evaluation of the unsigned enumeration values, #108766 (PR #108769)

[Jannick Kremer via cfe-commits]

https://github.com/DeinAlptraum approved this pull request.

Rest looks good to me.

Regarding releases, I'm not too familiar with the process here, but I believe backports aren't done unless it's a critical security bug or similar. @Endilll can you confirm, and do you also want to sign off on this? 

https://github.com/llvm/llvm-project/pull/108769