[Dune-devel] Update CI images and gitlab-ci templates

[Simon Praetorius]

Hi everyone,

in the last developer meeting it is decided to update the minimal
compiler requirements to clang5+ and gcc7+ and to activate c++17
standard by default.

Therefore, I have first added a CI template for the release 2.7: simply
include

https://gitlab.dune-project.org/core/ci-config/-/raw/master/config/common/releases/2.7.yml
https://gitlab.dune-project.org/core/ci-config/-/raw/master/jobs/common/releases/2.7.yml

in your `.gitlab-ci.yml` file to test your module with the compilers and
branches of release 2.7 (this is similar to the release 2.6 template,
but uses the latest compiler configuration used when building 2.7)

The templates for the master branch now can be updated to the new
compiler tests. The problem is, that there is no clang5 (c++17)
toolchain available in the docker images. And I'm not absolutely sure
where to change things in the docker/ci repository to add this
toolchain. I've submitted a MR but maybe those changes are not enough
and there was a discussion that maybe the creation of the docker images
is broken. So, I will not merge this until someone with more insight
into this gives the OK.

But, in the meantime one could at least update the template for the
.gitlab-ci.yml files and test everything with c++17 without the clang5
test. Therefore a MR is added

https://gitlab.dune-project.org/core/ci-config/-/merge_requests/2

There, the clang5 test is simply commented out and when the docker
images are updated it can be added back to the template.

Best wishes,
Simon

-- 
Dr. Simon Praetorius
Institut für Wissenschaftliches Rechnen
Fakultät Mathematik
Technische Universität Dresden
Tel.: TUD-34432
Mail: simon.praetorius at tu-dresden.de
Web: www.math.tu-dresden.de/~spraetor