Use the triple to figure out if this is a darwin target, not
the subtarget.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219673 91177308-0d34-0410-b5e6-96231b3b80d8
Grab the subtarget info off of the MachineFunction rather than
indirecting through the TargetMachine.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219674 91177308-0d34-0410-b5e6-96231b3b80d8