Added an "Interrupted" bit to the ProcessEventData. Halt now generates an event

with the Interrupted bit set.  Process::HandlePrivateEvent ignores Interrupted events.
DoHalt is changed to ensure that the stop even is processed, and an event with
the Interrupted event is posted.  Finally ClangFunction is rationalized to use this
facility so the that Halt is handled more deterministically.

llvm-svn: 119453