[InstSimplify] allow icmp with constant folds for splat vectors, part 2

Completes the m_APInt changes for simplifyICmpWithConstant().

Other commits in this series:
https://reviews.llvm.org/rL279492
https://reviews.llvm.org/rL279530
https://reviews.llvm.org/rL279534
https://reviews.llvm.org/rL279538



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279543 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed