verify-uselistorder: Reverse use-lists at every verification

Updated `verify-uselistorder` to more than double the number of use-list
orders it checks.

  - Every time it verifies an order, it then reverses the order and
    verifies again.

  - It now verifies the initial order, before running any shuffles.

Changed the default to `-num-shuffles=1`, since this is already four
checks, and after r214584 shuffling is guaranteed to make a new order.

This is part of PR5680.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214596 91177308-0d34-0410-b5e6-96231b3b80d8