Fix test on release builds.

Unfortunately I don't think there's a good way to validate branch targets on
release builds. Fortunately it's a minor part of this test (and based on
generic code) so I don't mind dropping it.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@186398 91177308-0d34-0410-b5e6-96231b3b80d8