Don't cache the TargetLoweringInfo object inside of the FunctionLowering object.

The TargetLoweringInfo object is owned by the TargetMachine. In the future, the
TargetMachine object may change, which may also change the TargetLoweringInfo
object.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183356 91177308-0d34-0410-b5e6-96231b3b80d8