Add ApplePropertyString dump helper to Dwarf.{h|cpp}.

Reviewers: dblaikie

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5688

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219442 91177308-0d34-0410-b5e6-96231b3b80d8