For now: newest version, newer than upstream spack.

Get rid of fxdiv, too…

Now we also modify the `SPACK_`-prefixed stuff for the spack compiler
wrappers.

This adds googletest's lib/lib64 isntall folder explicitly to the list
of libraries (it should have been found… but wasn't).

This reverts merge request !115

This reverts commit 6394d7dc

This reverts commit a17efe7a

* a few commits in pynn-brainscales (2), grenade (2), halco (2), hxcomm
  (2), haldls (1), hwdb (1)
  * add interface-draft for plasticity rules
  * support for requestion server-side information
    (`get_bitfile_info` and `get_repo_state`)
* also cleans up the tag mess in the dependent repositories…
  really same tag everywhere
* same for oppulance; as software state didn't change, we don't require
  oppulance to match pynn-brainscales version (rc2 is sufficient)…
  relaxing constraint, rc2

This reverts merge request !105

Let's try to find all build problems in one try… keep building after
the initial error to find additional ones.

This should fix the error about an ambiguous template instantiation
for 'struct halco::common::detail::limits<
halco::hicann_dls::vx::v1::SynapseOnSynapseRow, void>' which isn't
triggered on newer g++s. We dropped support for old `v1` hardware; this
was planned anyways.

This reverts merge request !104

Includes a missing header fix in hxcomm@ebrains-2.0-rc3

This reverts merge request !103