[SelectionDAG] Add a SDTCisSameSizeAs type constraint that can be used to ensure vector widths match even if the element size and count don't.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254138 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed