DwarfDebug: Prevent DebugLocEntry merging from coalescing two different
constants into only the first one.

rdar://14874886.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205357 91177308-0d34-0410-b5e6-96231b3b80d8
Add a comment about the DIDescriptor class hierarchy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205358 91177308-0d34-0410-b5e6-96231b3b80d8