Breakpad: Parse Stack CFI records

Summary:
This patch adds support for parsing STACK CFI records from breakpad
files. The expressions specifying the values of registers are not
parsed.The idea is that these will be handed off to the postfix
expression -> dwarf compiler, once it is extracted from the internals of
the NativePDB plugin.

Reviewers: clayborg, amccarth, markmentovai

Subscribers: aprantl, lldb-commits

Differential Revision: https://reviews.llvm.org/D60268

llvm-svn: 357975