#2470: submit cactuBSSN for SPEC v8 CPU benchmark

Comment (by Roland Haas):

For the SPECv8 contribution we had at one point mentioned 3 options
that we could propose:

McLachlan's ccZ4 formulation (in master)
McLachlan's Z4c formulation (in rhaas/Z4c)
a version of McLachlan that pre-computes all derivatives as grid
functions the way that the CUDA code does (in
rhaas/separatedderivatives)

Please use this form:

to voice preference for one or the other.

At this point none have been extracted and incorporated into the
min-driver used for SPEC.