Add missing includes for compilation with libc++

libc++ doesn't pull in some of the headers implicitly included by libstdc++, causing compilation to fail. This adds the required explicit #include statements.

Ah, this isn't my problem, it's somehow related to the new test selection stuff. @joe?

@joe: Can you take a look at the failing builds for Ubuntu? There seems to be a problem selecting tests to run...

The CI issue should be fixed by https://gitlab.math.tu-dresden.de/ansgar/dune-docker/commit/4ab8abe86d65f00ab369928ba784bfb5c1cd3fbd

Takes a bit more to rebuild & upload the updated images.

merged

mentioned in commit 85265016

Uh, this seems to have been resolved, right?