[llvm] [IRMover] Don't consider opaque types isomorphic to other types (PR #138241)

[Jay Foad via llvm-commits]

jayfoad wrote:

> Ping :)

Sorry I don't understand this code well enough to review it properly, but I'd be happy to accept it anyway based on trusting the author, simplifying the code, and not breaking any tests :)

https://github.com/llvm/llvm-project/pull/138241