[llvm] [AArch64][LoopVectorize] Use either fixed-width or scalable VF when tail-folding (PR #67543)

[David Sherwood via llvm-commits]

https://github.com/david-arm commented:

Thanks for this @rin-arm! It's almost there. I just have a few minor comments about improving the new test to make it more robust and cleaner.

https://github.com/llvm/llvm-project/pull/67543