Watchpoint WIP:

o WatchpointLocationList:
  Add a GetListMutex() method.
o WatchpointLocation:
  Fix Dump() method where there was an extra % in the format string.
o Target.cpp:
  Add implementation to CreateWatchpointLocation() to create and enable a watchpoint.

o DNBArchImplX86_64.cpp:
  Fix bugs in SetWatchpoint()/ClearWatchpoint() where '==' was used, instead of '=',
  to assign/reset the data break address to a debug register.

  Also fix bugs where a by reference debug_state should have been used, not by value.

llvm-svn: 139666