[llvm] [VectorCombine] Fix scalarizeExtExtract for big-endian (PR #157962)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@uyoyo0 please can you raise an issue for this so we can track it - we probably want to backport this to 21.x

https://github.com/llvm/llvm-project/pull/157962