[X86] Pre-SSE42 v2i64 sgt lowering - check if representable as v2i32 (#83560)

Without PCMPGTQ, if the i64 elements are sign-extended enough to be representable as i32 then we can compare the lower i32 bits with PCMPGTD and splat the results into the upper elements.

Value tracking has meant we already get pretty close with this, but this allows us to remove a lot of unnecessary bit flipping.