[llvm] [Hexagon/LoopIdiom] Protect test against O2 changes (PR #144734)

[Nikita Popov via llvm-commits]

nikic wrote:

@kparzysz There is some ongoing work for that here: https://github.com/llvm/llvm-project/pull/140301

@artagnon I think it's okay if you just add a triple check for hexagon for now, until it can be integrated into LIR.

https://github.com/llvm/llvm-project/pull/144734