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

[Teresa Johnson via llvm-commits]

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teresajohnson wrote:

I'm unsure of why this test is not affected by this patch then - wouldn't we now keep `%A.11` in the merged module for `@g2`?

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