[X86][SSE] Add 'vectorized sum' test patterns

These are often generated when building a vector from the reduction sums of independent vectors.

I've implemented some typical patterns from various v4f32/v4i32 based off current codegen emitted from the vectorizers, although these tests are more about tweaking some hadd style backend folds to handle whatever the vectorizers/vectorcombine throws at us...

Author: RKSimon