[NFC][SimplifyCFG]Precommit test case to show inner-loop metadata may not be preserved

- There is an outer while-loop and an inner for-loop in the test case.
  Inner-loop has `llvm.loop.unroll.enable` metadata that is not
  preserved. This happens around [1], when the loop metadata of outer loop
  overrides the inner loop metadata directly, without looking at whether inner-loop
  itself has loop metadata.

 [1] https://github.com/llvm/llvm-project/blob/ab755e65629ea098cb6faa77b13ac087849ffc67/llvm/lib/Transforms/Utils/Local.cpp#L1146

Differential Revision: https://reviews.llvm.org/D134014