internal nodes with flag results. Record these with a new
OPC_MarkFlagResults opcode and use this to update the interior
nodes' flag results properly. This fixes CodeGen/X86/i256-add.ll
with the new isel.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97021 91177308-0d34-0410-b5e6-96231b3b80d8