[clang] [clang] fix obtaining underlying type for demoted enum definitions (PR #155900)

[James Y Knight via cfe-commits]

jyknight wrote:

Hi -- sidenote, but I noticed that this commit -- and many other of your commits -- are missing the entire commit message other than the PR title. I don't know if that's a github preference or something you're doing manually, but it's really unfortunate because then I cannot see the explanations in git log -- instead needing to indirect through the PR page. 

Do you know why that's happening for your changes?

https://github.com/llvm/llvm-project/pull/155900