Vulkan has multiple synchronization objects:
- Events, which provide synchronization between commands submitted
  to the same queue, or between the host and a queue.
- Fences, which insert a dependency from a queue to the host
- Semaphores, which insert a dependency between batches submitted
  to queues

For now, SwiftShader will treat these synchronization primitives as noop, since:
- Commands will be executed in order
- SwiftShader currently only supports 1 queue

Change-Id: Ic335e2f7aa30ab7314bf7585e11f1f30a79f50d6
Reviewed-on: https://swiftshader-review.googlesource.com/c/21588Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>