[clang] [clang][codegen] Mention the invariant that LLVM demangler should be … (PR #117346)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Yes, review comments don't indicate approval after the comments are addressed unless the reviewer explicitly says that.  The reviewer may want to take a look at the updated changes, or responses to review comments, or maybe the review wasn't complete for whatever reason.

That said, given it's just a comment change, I'm okay with leaving it in-tree until @jyknight follows up on the review.

https://github.com/llvm/llvm-project/pull/117346