Add a triple to test/DebugInfo/unconditional-branch.ll (PR23252)

This started failing on Windows after my switch lowering change in r235101.

I suspect the error is unrelated, so adding a triple to pacify it
until it can be fixed. See the PR for details.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235106 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed