[llvm-dwp] Adding support for v5 index writing

This patch adds general support for DWARFv5 index writing.
In particular, this means only allowing inputs with one version,
either DWARFv5 or DWARFv4.

This patch adds the .debug_macro section as an example,
but the DWARFv5 type support and loc and rangelists are still
missing (and upcoming).

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D102315