[DWARF} Use LLVM's debug line parser in LLDB.

The line number table header was substantially revised in DWARF 5 and is
not fully supported by LLDB's current debug line implementation.

This patch replaces the LLDB debug line parser with its counterpart in
LLVM. This was possible because of the limited contact surface between
the code to parse the DWARF debug line section and the rest of LLDB.

We pay a small cost in terms of performance and memory usage. This is
something we plan to address in the near future.

Differential revision: https://reviews.llvm.org/D62570

llvm-svn: 368742