UseListOrder: Additional test coverage for r214242

r214242 was subtle enough it really deserves a targeted test with
comments.  This adds some global variables that trigger the relevant
code path.  Sorry this wasn't committed with the fix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214243 91177308-0d34-0410-b5e6-96231b3b80d8