Rework fix in r201744. You really DO need to waitpid twice to get the

process fully reaped.  The race & bad behavior was because we were letting
the reaping thread in LLDB to also set the Process exit status, so debugserver
would sometimes be shut down before it got a chance to report the exit status, 
and then we got confused.

<rdar://problem/16555850>

llvm-svn: 211636