[llvm-xray] Add AArch64 to llvm-xray extract

This required adding support for resolving R_AARCH64_ABS64 relocations to
get accurate addresses for function names to resolve.

Authored by: ianlevesque (Ian Levesque)
Reviewers: dberris, phosek, smeenai, tetsuo-cpp
Differential Revision: https://reviews.llvm.org/D69967