The package should contain the cxx standards

[LecrisUT]

Not sure how to do it in spack, but it would be helpful to bail-out immediately if the compiler does not support the cxx standards (over here being c++14), i.e. before it starts to compile the dependencies.

(Similar configuration should be added to libxc as well (c90))

[fangohr]

Which dependency of Octopus needs c++14 (if this is still an issue)?