swift234

[driver] Updated Compilation::performJobsInList() to properly handle Commands which depend on peers.

Across recursive calls to performJobsInList(), keep track of ScheduledCommands
and FinishedCommands, so we can do the following:

  - Don’t schedule a Command which is already scheduled (since it may be
    scheduled as a peer before we try to schedule it as an input).
  - Don’t schedule a Command whose inputs have not all finished.

Swift SVN r12444