[Bug c++/124246] [reflection] is_swappable_type doesn't work with std::priority_queue

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124246

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Note that if I uncomment the first assert, the whole test then works.  It also
works if I add

template class std::priority_queue<int>;

before the second static_assert.  Also observe that this works fine:

```
#include <meta>
#include <queue>

static_assert (std::meta::is_swappable_type (^^std::queue <int>));
```