Watchpoint work in progress:

Add a virtual method GetHardwareWatchpointHit() to the DNBArchProtocol base class
which consults the architecture to return the watchpoint hit; otherwise return an
invalid index.

Add impl. of the method to X86_64 and I386 subclasses, plus reset the debug status
register before we resume execution of the inferior thread.

llvm-svn: 139034