[clang] [llvm] [X86] Fix LowerFunnelShift crash when folding yields BUILD_VECTOR (PR #233070)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

Apologies @m-amirpour but I missed this (but please bear in mind that I had taken the assignment and you hadn't even commented on #233063) - I've raised #233077 which allows splitVectorOp to handle such cases in a more general manner instead of just adding the early out in your patch. 

https://github.com/llvm/llvm-project/pull/233070