Adds a new lit directive to improve C++ Standard filtering. This is based on the [Discourse](https://discourse.llvm.org/t/rfc-improving-c-standard-filtering-in-the-lit-tests/78474) discussion.
Adds a new lit directive to improve C++ Standard filtering. This is based on the [Discourse](https://discourse.llvm.org/t/rfc-improving-c-standard-filtering-in-the-lit-tests/78474) discussion.