petsc: explicitly disable X11 (#2533)
petsc: explicitly disable X11 (#2533)

otherwise petsc may pickup libX11 on login nodes during config/build,
but libX11 may not be available on computation nodes.
lgarren/spack,iulian787/spack,mfherbst/spack,skosukhin/spack,EmreAtes/spack,skosukhin/spack,mfherbst/spack,LLNL/spack,tmerrick1/spack,krafczyk/spack,LLNL/spack,matthiasdiener/spack,TheTimmy/spack,tmerrick1/spack,skosukhin/spack,iulian787/spack,matthiasdiener/spack,EmreAtes/spack,TheTimmy/spack,tmerrick1/spack,matthiasdiener/spack,EmreAtes/spack,lgarren/spack,krafczyk/spack,iulian787/spack,lgarren/spack,krafczyk/spack,TheTimmy/spack,krafczyk/spack,mfherbst/spack,LLNL/spack,matthiasdiener/spack,iulian787/spack,TheTimmy/spack,EmreAtes/spack,skosukhin/spack,tmerrick1/spack,LLNL/spack,mfherbst/spack,skosukhin/spack,krafczyk/spack,mfherbst/spack,tmerrick1/spack,lgarren/spack,matthiasdiener/spack,iulian787/spack,LLNL/spack,TheTimmy/spack,lgarren/spack,EmreAtes/spack