Push DwarfDebug::attachRangesOrLowHighPC down into DwarfCompileUnit

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219372 91177308-0d34-0410-b5e6-96231b3b80d8
Remove uses of the TargetMachine from FunctionLoweringInfo
via caching TargetLowering and using the MachineFunction.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219375 91177308-0d34-0410-b5e6-96231b3b80d8