D9049: Compile with stricter compilation flags

[David Faure]

dfaure accepted this revision.
This revision is now accepted and ready to land.

REPOSITORY
  R263 KXmlGui

BRANCH
  fix_strict_compile

REVISION DETAIL
  https://phabricator.kde.org/D9049

To: mlaurent, dfaure
Cc: apol, #frameworks