[InstCombine] Fix constant-folding of overflowing arithmetic ops on vectors

Feeding vector values to `InstCombiner::OptimizeOverflowCheck` produces a scalar boolean flag if it proves the overflow check can be eliminated.
This causes `InstCombiner::CreateOverflowTuple` to crash as it correctly expects a vector of i1 values instead.

Reviewed By: lebedev.ri

Differential Revision: https://reviews.llvm.org/D89628