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

[Devon Loehr via cfe-commits]

DKLoehr wrote:

Because this warning keeps firing in many different places, including in third-party libraries, I've disabled it by default until I can go through and fix all the instances. I think this provides a cleaner separation of concerns, so that this PR isn't clogged up with various housekeeping changes. Once the warning is cleaned up, it should be enabled-by-default.

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