Recommit "Add a verbose mode to "image dump line-table" and use it to write a .debug_line test"

This reapplies r350802, which was reverted because of issues with
parsing posix-style paths on windows hosts (and vice-versa). These have
since been fixed in r351328, and lldb should now recognise the path
style used in a dwarf compile unit correctly.

llvm-svn: 351435