DWARFDebugLoclists: stricter base address handling

Summary:
This removes the use of zero as a base address in section-based dumping.
Although this will often be true for (unlinked) object files with a
single compile unit, it is not true in general. This means that
section-based dumping will not be able to resolve entries referencing
the base address (DW_LLE_offset_pair) -- it wasn't able to do that
correctly before either, but now it will be more explicit about it. One
exception to that is if the location list contains an explicit
DW_LLE_base_address entry -- in this case the dumper will pick it up,
and resolve subsequent entries normally.

The patch also removes the fallback to zero in the "inline" dumping in
case the compile unit does not contain a base address.

Reviewers: dblaikie, probinson, JDevlieghere, aprantl, SouraVX

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70115