[llvm] [NFC][LoopDistribute] Add test for doubly nested loop (PR #179263)

[Madhur Amilkanthwar via llvm-commits]

madhur13490 wrote:

> What is the purpose of this test? To eventually also distribute the outer loop?

Yes, eventually...some day. However, at this point, it conveys the fact that the current loop distribution can handle nested loops and does not necessarily require just loops of depth 1. There is no test in `Transforms/LoopDistribute/` which has loop of nest > 1.

https://github.com/llvm/llvm-project/pull/179263