DebugInfo: DIBuilder changes to match DIEnumerator changes in r184694

Representing enumerators by int64 instead of uint64 for now. At some
point we need to address the underlying issue of representation
depending on the specific enumeration.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184761 91177308-0d34-0410-b5e6-96231b3b80d8