[driver] Fixed a bug in DummyTaskQueue where it would not generate un…

…ique ProcessIds.

Since DummyTaskQueue does not actually execute, it keeps a counter of
ProcessIds. This previously was a local variable; it is now static since
multiple instances of DummyTaskQueue may be used, depending on the requested
commands.

No tests for this yet, but this will be required to properly test parseable
output.

Swift SVN r20849

lib/Basic/TaskQueue.cpp

@@ -50,12 +50,12 @@ void DummyTaskQueue::addTask(const char *ExecPath, ArrayRef<const char *> Args,
 bool DummyTaskQueue::execute(TaskQueue::TaskBeganCallback Began,
                              TaskQueue::TaskFinishedCallback Finished,
                              TaskQueue::TaskSignalledCallback Signalled) {
-  typedef std::pair<pid_t, std::unique_ptr<DummyTask>> PidTaskPair;
+  typedef std::pair<ProcessId, std::unique_ptr<DummyTask>> PidTaskPair;
   std::queue<PidTaskPair> ExecutingTasks;
 
   bool SubtaskFailed = false;
 
-  pid_t Pid = 0;
+  static ProcessId Pid = 0;
 
   unsigned MaxNumberOfParallelTasks = getNumberOfParallelTasks();