Update clang-format to version 10

[jcoupey]

The current formatting script rely on finding version 6.0 of clang-format, which is not available out of the box any more on recent distros.

We should update to version 10.0. I hope this won't lead to too many unsolicited formatting changes.

[jcoupey]

Pretty straightforward update, turns out the only changes applied where leftovers from a non-formatted PR merged recently.