SelectionDAGISel::CreateScheduler, and make it just create the
scheduler. Leave running the scheduler to the higher-level code.
This makes the higher-level code a little more explicit and
easier to follow, and will help enable some future refactoring.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@63944 91177308-0d34-0410-b5e6-96231b3b80d8