LLVMTargetMachine/TargetPassConfig: Simplify handling of start/stop options; NFC

- Make some TargetPassConfig methods that just check whether options have
  been set static.
- Shuffle code in LLVMTargetMachine around so addPassesToGenerateCode
  only deals with TargetPassConfig now (but not with MCContext or the
  creation of MachineModuleInfo)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345918 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed