Restrict OpenMP and OpenACC offloading intrinsics

[sergisiso]

Currently we allow most Fortran intrinsics to be offloaded to GPUs with OpenMP and OpenACC directive, but not all of them are supported in GPUs. However, the standards are not clear which ones are supported and which are not. Is this compiler implementation dependent?

For nvfortarn OpenACC there is https://docs.nvidia.com/hpc-sdk/compilers/hpc-compilers-user-guide/#acc-fort-intrin-sum , but I haven't found explicit list for other compilers yet.