Track whether a process was Launched or Attached to. If Attached, the detach...

Track whether a process was Launched or Attached to.  If Attached, the detach when the debugger is destroyed, rather than killing the process.  Also added a Debugger::Clear, which gets called in Debugger::Destroy to deal with all the targets in the Debugger.  Also made the Driver's main loop call Destroy on the debugger, rather than just Destroying the currently selected Target's process.

llvm-svn: 139852