Fix new.clcpp test

`new.clcpp` doesn't compile under clang-12, or newer versions, due to a bug. It needs to be addressed to allow for automated building and testing of libclcxx and for Github actions workflow to function.

Start with the new.clcpp test and reproduce its compilation failure using clang-12 or a newer version. Identify the reported bug and address it so the test compiles, automated libclcxx building and testing work, and the GitHub Actions workflow functions.

Written by the indexing model from the issue text.