[SystemZ] Add DebugInfo test cases

This adds all DebugInfo tests for the SystemZ target.

This version of the patch incorporates feedback from reviews by
Eric Christopher and Rafael Espindola.  Thanks to all reviewers!

Patch by Richard Sandiford.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@181205 91177308-0d34-0410-b5e6-96231b3b80d8