auto allowed with a type in C++

We currently allow something like this in C++: https://godbolt.org/z/7fabbGfe6

```cpp
void f() {
auto int x = 1;
}
```

It looks like this was allowed as an extension in C++ because it was valid C but I don't think it makes sense to support this anymore.

Start by reproducing the `auto int x = 1` example from the Godbolt link in the C++ compiler. Trace where this construct is accepted and look for the relevant compiler tests; done means the construct is rejected in C++ while the existing C behavior remains covered.

Written by the indexing model from the issue text.