Debug Info Testing: Updated to use null instead of "i32 0" for containing-type
field of DICompositeType.

This will help the follow-on patch of using DITypeRef for containing-type field.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190187 91177308-0d34-0410-b5e6-96231b3b80d8