[llvm] [X86] Use an FP-based expansion for v4i32 ctlz on SSE2-only targets (PR #167034)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

vXi32 types must be converted to vXf64 - not vXf32 - only smaller types (or if you can prove the upper 16 bits are zero) can use vXf32

https://github.com/llvm/llvm-project/pull/167034