[llvm] [X86] Check if machine loop is passed while getting loop alignment (PR #77283)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

This is needed for #77264. Opened this as a separate PR as I wanted to confirm this is appropriate use of the API with X86 maintainers. There is at least one call to `getPrefLoopAlignment` inside the ARM backend that doesn't pass a `MachineLoop`, but nothing in X86. Given that, I think this makes sense, but wanted to confirm.

https://github.com/llvm/llvm-project/pull/77283