[llvm] [DropUnnecessaryAssumes] Make the ephemeral value check more precise (PR #160700)

[Ramkumar Ramachandra via llvm-commits]

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

After some more thought, I think a collectUsersRecursively is probably not the best idea. LGTM, thanks!

https://github.com/llvm/llvm-project/pull/160700