Get HOMMEXX building in CAM

There are a few things which need to be done before this can happen
- [X] Add `preqx_cxx` to the list of valid values for `CAM_TARGET`
- [X] Add the list of directories containing the sources to the `write_filepath` function in CAM's configuration when `dyn_target` is `preqx_cxx`
- [X] Add Kokkos' build information to the configuration settings
- [X] Enable building the C++ without `Hommexx_config.h`
- [X] Ensure CAM calls the C++ in the main timestepping loop
- [X] Ensure all the defines needed are specified (QSIZE_D, PLEV, etc)
- [X] Ensure vectorization settings are specified correctly (ie, `-xCORE_AVX512`)
- [X] Ensure HOMMEXX picks the correct explicit vector type
- [ ] Ensure the Kokkos forcing method implementations are called
- [ ] Ensure Kokkos initialization methods are called
- [ ] Ensure Kokkos finalization methods are called
- [ ] Ensure the MPI communicator is set correctly
- [X] Ensure all data needed is copied - this should be done somewhere in the `prim_run_subcycle` subroutine's code path
- [ ] Other issue?