When jobs waiting for a dependency are notified, they're re-added to the
queue. This would require owning the queue lock in exclusive mode, but
since the function doing so is called from within the job/opcode
processor, it only holds the lock in shared mode.

This patch changes the result of the processor from a boolean to a
status value (integer). This way the caller can be notified about
actions to take, including notifying waiting jobs. The function adding
jobs to the queue can now acquire the lock in exclusive mode.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>