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
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