Add all the 'generic' architectures that are mentioned in recipes (#12958)
Add all the 'generic' architectures that are mentioned in recipes (#12958)

LLVM, mesa and other packages check for these generic
microarchitectures. One solution is to let Spack know they exist.
iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack