Accept DWARF version 2 and 3 in debug_line tables

Issue reported by Matthew Gardiner.  Further work is necessary to
synchronize LLDB's DWARF classes with the derivatives now in LLVM.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@205771 91177308-0d34-0410-b5e6-96231b3b80d8