DebugInfo: Fix argument ordering in test by adding argument numbering.

This old test didn't have the argument numbering that's now squirelled
away in the high bits of the line number in the DW_TAG_arg_variable
metadata.

Add the numbering and update the test to ensure arguments are in-order.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209669 91177308-0d34-0410-b5e6-96231b3b80d8