hold a strong pointer to that extended backtrace thread in the Process
just like we do for asking a thread's extended backtrace.
Also, give extended backtrace threads an invalid ThreadIndexID number.
We'll still give them valid thread_id's. Clients who want to know the
original thread's IndexID can call GetExtendedBacktraceOriginatingIndexID().
<rdar://problem/16126034>
llvm-svn: 203088
Still working out some of the details of these classes but
I wanted to get the overall structure checked in.
<rdar://problem/15314068>
llvm-svn: 194245
Jason Molenda