Properly diagnose using abstract and incomplete types in va_arg

- Move a test from test/SemaTemplate/instantiate-expr-3.cpp, it did not belong there
- Incomplete and abstract types are considered hard errors


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@132979 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed