[clang][Interp] Lazily visit constant locals in C++

While we _do_ get them registered via visitInitializer(), they
are still local, so gone on the next call to e.g. evaluateAsRValue().

Visit them lazily, similarly like we do in C.

GitOrigin-RevId: a52c0c770056e040390839e753dbbaccbf4d63c4
2 files changed