D13394: C++: update for c++20 and fix some syntax errors

[Christoph Cullmann]

cullmann added a comment.


  Will take a look ;=)

REPOSITORY
  R216 Syntax Highlighting

REVISION DETAIL
  https://phabricator.kde.org/D13394

To: jpoelen, dhaumann
Cc: cullmann, kde-frameworks-devel, michaelh, ngraham, bruns