This PR replaces some instances of `undef` with `function argument value` or `poison` or `concrete values` in several tests under `llvm/test/Transforms/` directory. These changes align with modern LLVM standards for better-defined behavior and test determinism. If this small PR is okay and gets merged, I will work on the rest. This is inspired by [this project](https://discourse.llvm.org/t/gsoc-2024-remove-undefined-behavior-from-tests/77236/29), work done on this by @leewei05