[llvm] [ExpandReductions] Add support for non-pow2 vector counts (PR #208738)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> @RKSimon Regenerated the failing tests.

@Prajwal-kp-18 Please remember to re-request reviews when you're ready to be reviewed again - ping notifications alone can get lost in the github firehose

https://github.com/llvm/llvm-project/pull/208738