you to do things like:
/// PointerUnion<int*, float*> P;
/// P = (int*)0;
/// printf("%d %d", P.is<int*>(), P.is<float*>()); // prints "1 0"
/// X = P.get<int*>(); // ok.
/// Y = P.get<float*>(); // runtime assertion failure.
/// Z = P.get<double*>(); // does not compile.
/// P = (float*)0;
/// Y = P.get<float*>(); // ok.
/// X = P.get<int*>(); // runtime assertion failure.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@67987 91177308-0d34-0410-b5e6-96231b3b80d8
