[hwasan] Offline symbolization script.

Summary:
A script to symbolize hwasan reports after the fact using unstripped
binaries. Supports stack-based reports. Requires llvm-symbolizer
(addr2line is not an option).

Reviewers: pcc, hctim

Subscribers: mgorny, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D71148