Update the clang compiler definition to use IBM XL Fortran compiler (#8389)
Update the clang compiler definition to use IBM XL Fortran compiler (#8389)

on CORAL systems (linux-rhel7-ppc64le).
mfherbst/spack,matthiasdiener/spack,LLNL/spack,iulian787/spack,matthiasdiener/spack,krafczyk/spack,matthiasdiener/spack,iulian787/spack,matthiasdiener/spack,matthiasdiener/spack,iulian787/spack,mfherbst/spack,LLNL/spack,mfherbst/spack,mfherbst/spack,LLNL/spack,krafczyk/spack,mfherbst/spack,LLNL/spack,LLNL/spack,iulian787/spack,krafczyk/spack,iulian787/spack,krafczyk/spack,krafczyk/spack