DebugInfo: Provide a utility for building a mapping from llvm::Function*s to llvm::DISubprograms

Update DeadArgumentElimintation to use this, with the intent of reusing
the functionality for ArgumentPromotion as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212122 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the use and initialization of the target machine and subtarget
from SystemZFrameLowering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212123 91177308-0d34-0410-b5e6-96231b3b80d8
Move the subtarget dependent features from SystemZTargetMachine
down to the subtarget. Add an initialization routine to assist.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212124 91177308-0d34-0410-b5e6-96231b3b80d8