[clang] [clang][Builtins] Parse clang extended vectors types. (PR #83584)

[Francesco Petrogalli via cfe-commits]

fpetrogalli wrote:

Other C++ compatible option: provide a family of templates, one for each number of lanes, templated on the type:

```
_ExtVector_N<T>
```

So that we need up having:

```
_ExtVector_2<double>
_ExtVector_6<unsigned int>
...
```

This would be pretty easy to handle, without introducing extra complications in the parser.

https://github.com/llvm/llvm-project/pull/83584