llvm-dwarfdump: type unit dwo support

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198850 91177308-0d34-0410-b5e6-96231b3b80d8
Prototype of skeleton type units for fission

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198851 91177308-0d34-0410-b5e6-96231b3b80d8