Fixed an issue where we would try to interrupt a process while it is in the process of naturally stopping due to another reason (breakpoint, or step).

Added a new MachProcess::Interrupt() which correctly tracks such cases and "does the right thing".

<rdar://problem/16593556>



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@207139 91177308-0d34-0410-b5e6-96231b3b80d8