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>


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@211636 91177308-0d34-0410-b5e6-96231b3b80d8