[InstCombine] use m_APInt to allow icmp (trunc X, Y), C folds for splat constant vectors

This is a sibling of:
https://reviews.llvm.org/rL278859
https://reviews.llvm.org/rL278935
https://reviews.llvm.org/rL278945
https://reviews.llvm.org/rL279066
https://reviews.llvm.org/rL279077
https://reviews.llvm.org/rL279101


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279133 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed