Fix gpu ci

What is the bug

The nvhpc_gpu CI is not actually compiling with CUDA.

How do you fix it

Fix the pipeline and some bugs in the code.

• std::cerr and std::exit are host-only functions and should not be called from a kernel.
• gtest_discover_tests emulates the code so it requires code execution environment. The Levante CI runs in shared partition, which does not have GPUs.

How urgent is the bugfix

• I need it as soon as possible
• I can wait for a couple of days
• None of my current codes is directly affected

Mandatory steps before review

• Gitlab CI passes (Hint: use make format for linting)
• Bugfix is covered by additional unit tests
• Mark the merge request as ready by removing Draft:

Mandatory steps before merge

• Reviewed by a maintainer
• Incorporate review suggestions
• Remember to edit the commit message and select the proper changelog category (feature/bugfix/other)
• Prior to merging, please remove any boilerplate from the MR description, retaining only the What is the bug and How do you fix it section to maintain

You are not supposed to merge this request by yourself, the maintainers of libiconmath take care of this action!