Add minidump support to obj2yaml

Summary:
This patch adds the code needed to parse a minidump file into the
MinidumpYAML model, and the necessary glue code so that obj2yaml can
recognise the minidump files and process them.

Reviewers: jhenderson, zturner, clayborg

Subscribers: mgorny, lldb-commits, amccarth, markmentovai, aprantl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59634

llvm-svn: 357469