Modify the delegation chain from MachThreadList -> MachThread -> DNBArchProtocol so that when

the watchpoint state is changed, not only does the change propagate to all the thread instances,
it also updates a global debug state, if chosen by the DNBArchProtocol derivative.

Once implemented, the DNBArchProtocol derivative, also makes sure that when new thread comes along,
it tries to inherit from the global debug state, if it is valid.

Modify TestWatchpointMultipleThreads.py to test this functionality.

llvm-svn: 140811