Comment (by Erik Schnetter):

You would need to point Spack to the compiler and MPI libraries that it should use (and maybe a few more), and then build the rest. Building your own MPI library is easy; using it is next to impossible since it’s very difficult to configure it to use the existing hardware (and it’s probably actually impossible on Crays).

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2553/cactus-link-command-uses-cppflags-and