[llvm] [JumpThreading] Don't phi translate past loop phi (PR #70664)

[via llvm-commits]

alexfh wrote:

Thanks! This fixes the original problem that led to the report in https://github.com/llvm/llvm-project/commit/b22917e6e2a0aec05474f58e64b7e87d1ea0a054#commitcomment-131124585.

https://github.com/llvm/llvm-project/pull/70664