[llvm] [LoopUnroll] Remove `computeUnrollCount()`'s return value (PR #184529)

[Justin Fargnoli via llvm-commits]

justinfargnoli wrote:

Hi @mikaelholmen, thanks for bringing this up and providing such a succinct test case! 

> Is this as expected?

No, this is not expected behavior.  

I've put up a hot fix with #187034, and if this is too urgent, I've also put up a straight revert with #187035. 

https://github.com/llvm/llvm-project/pull/184529