Add Atom Silvermont (slm) tests

- check that -mcpu=slm uses the call register indirect optimization
- check that -mcpu=slm runs the scheduler 
- check that -mcpu=slm supports the movbe instruction



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190814 91177308-0d34-0410-b5e6-96231b3b80d8