compiler: make default openmp_flag() and cxx11_flag() die when these properties are not implemented in a derived class
compiler: make default openmp_flag() and cxx11_flag() die when these properties are not implemented in a derived class

iulian787/spack,iulian787/spack,mfherbst/spack,matthiasdiener/spack,TheTimmy/spack,krafczyk/spack,EmreAtes/spack,iulian787/spack,LLNL/spack,EmreAtes/spack,TheTimmy/spack,TheTimmy/spack,tmerrick1/spack,lgarren/spack,lgarren/spack,matthiasdiener/spack,LLNL/spack,mfherbst/spack,skosukhin/spack,krafczyk/spack,iulian787/spack,LLNL/spack,mfherbst/spack,skosukhin/spack,TheTimmy/spack,LLNL/spack,tmerrick1/spack,matthiasdiener/spack,skosukhin/spack,lgarren/spack,krafczyk/spack,matthiasdiener/spack,iulian787/spack,skosukhin/spack,LLNL/spack,skosukhin/spack,tmerrick1/spack,EmreAtes/spack,mfherbst/spack,EmreAtes/spack,EmreAtes/spack,krafczyk/spack,tmerrick1/spack,mfherbst/spack,lgarren/spack,lgarren/spack,matthiasdiener/spack,tmerrick1/spack,TheTimmy/spack,krafczyk/spack