nvhpc-only environment won't work because of xz package

[Anton Kozhevnikov]

This is a simplified DFT dev.env https://github.com/eth-cscs/alps-spack-stacks/tree/main/pe-dft-nvhpc

It won't work becuase spack install xz%nvhpc won't work.

[Ben Cumming]

An additional gcc compiler is needed to build the dependencies that can't be built by the nvhpc toolchain, such as xz.

Out of curiosity, does xz%nvhpc not work because it tries to build with nvhpc and fails?

    nvhpc-env:
      compiler:
          - toolchain: llvm
            spec: nvhpc@22.11
          - toolchain: gcc
            spec: gcc@11
      unify: true
      specs:
      - libxc%nvhpc
      - cuda%gcc
      - cmake%gcc
      - intel-oneapi-mkl+cluster%nvhpc
      - quantum-espresso%nvhpc +cuda +libxc ^intel-oneapi-mkl+cluster
      - xc%gcc
      mpi:
          spec: cray-mpich-binary
          gpu: Null
      packages:
      - perl
      - git