Missing Clang 16 support

[andreasfertig]

Clang 16 support for C++ Insights is missing at the moment due to the following reasons:

1. LLVM seems to no longer provide pre-built binaries for macOS Intel
2. Some API changes in LLVM/Clang (as usual) need adjustments to the C++ Insights code.
3. Some changes require additional work in C++ Insights and it's unclear whether the change is intended. For example, compiler-explorer.com/z/3WhM9odP9:

struct Test
{
    using size_type = int;

    size_type size() { return 5; }
};

auto X()
{
    Test s{};

    return s.size();
}

int main() {
    X();
}

The return type of X is Test::size_type in Clang 15 and size_type in Clang 16.

I got 1 and 2 covered by running my own build, and the API changes were also fixable, but I haven't had time to look into 3.

Andreas

[andreasfertig]

Fixed by #569.