Use HOST_ONLY macro instead of !define(CUDA) && !define(HIP)

[lucbv]

In a few spots the following logic has been implemented during the HIP backend work:
#if !defined(KOKKOS_ENABLE_CUDA) && !defined(KOKKOS_ENABLE_HIP)
one could probably replace that with
#if defined(KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST)
to selectively enable blocks of code when the compiler is not targeting a device or we could add the following macro in KokkosKernels_macros.hpp:

#if !defined(KOKKOS_ENABLE_CUDA) && !defined(KOKKOS_ENABLE_HIP)
#define KOKKOSKERNELS_HOST_ONLY
#endif

@brian-kelley do you have an opinion?

[brian-kelley]

@lucbv I don't think KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST is an exact replacement, since it is defined for host code in a cuda-enabled build (defined(KOKKOS_ENABLE_CUDA) && !defined(__CUDA_ARCH__)). I think adding the HOST_ONLY macro would make sense. Even better would be to avoid macros and use templated constexpr functions like kk_is_gpu_exec_space<ExecutionSpace>(), but I know that's not possible everywhere.

[lucbv]

Yeah, I think in the case of the trtri and trmm tests the compiler would just complain about the use of a host function in a device function so the macro is probably the right approach, but in other cases I do like the templated constexpr function approach. I will make a PR for the new macro tonight.