[clang] Warn when unique objects might be duplicated in shared libraries (PR #117622)

[Devon Loehr via cfe-commits]

DKLoehr wrote:

If a review was requested from you and this code isn't related, apologies: For some reason attempting to rebase onto the current state of the repo ended up including a bunch of random extra commits that aren't related, and that resulted in a bunch of people automatically being added as reviewers that I can't remove. Sorry for the inconvenience.

https://github.com/llvm/llvm-project/pull/117622