This is important for symbolizing executables with debug info in
unavailable .dwo files. Even if all DIE entries are missing, we can
still symbolize an address: function name can be fetched from symbol table,
and file/line info can be fetched from line table.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206665 91177308-0d34-0410-b5e6-96231b3b80d8
