DWARFDebugLoclists: Make it possible to read relocated addresses

Summary:
Handling relocations was not needed when the loclists section was a
DWO-only thing. But since DWARF5, it is possible to use it in regular
objects too, and the standard permits embedding addresses into the
section directly. These addresses need to be relocated in unlinked
files.

Reviewers: JDevlieghere, dblaikie, probinson

Subscribers: aprantl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68271