Guard a runtime error when building without MPI but with CUDA
ibarrier() in communicator.hpp does not support MPI right now. For now it's trying to throw an std::runtime_error in a function with return value which would cause nvcc refuses to build.
ibarrier() in communicator.hpp does not support MPI right now. For now it's trying to throw an std::runtime_error in a function with return value which would cause nvcc refuses to build.