[SelectionDAG] Add getTokenFactor, which splits nodes with > 64k operands.

This functionality is required at multiple places which potentially
create large operand lists, like SelectionDAGBuilder or DAGCombiner.

Differential Revision: https://reviews.llvm.org/D56739

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351552 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed