Synchronize LLVM and clang's ObjCDeclSpec::ObjCPropertyAttributeKind.

Synchronize LLVM and clang's ObjCDeclSpec::ObjCPropertyAttributeKind.

This adds Clang-specific DWARF constants for nullability and ObjC
class properties that are already generated by clang. This patch adds
dwarfdump support and a more comprehensive testcase.

<rdar://problem/27335745>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275354 91177308-0d34-0410-b5e6-96231b3b80d8