Add ExceptionStream to llvm::Object::minidump

Summary:
This will allow updating MinidumpYAML and LLDB to use this common
definition.

Reviewers: labath, jhenderson, clayborg

Reviewed By: labath

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68656

llvm-svn: 375239