After QTBUG-115583 reported that GCC's -Wredundant-decls got triggered in QPageSize, I tried adding that flag to headersclean. This brought to light that various QML_ macros contain a friend declaration for QML_REGISTER_TYPES_AND_REVISIONS. If a type such as QtGraph's QAbstractAxis contains more than one of these macros (in that case QML_FOREIGN and QML_UNCREATABLE), the friend declaration is duplicated in the macro expanded class declaration, triggering -Wredundant-decls.

Solutions could be to combine the macros, so only one is necessary (QML_UNCREATABLE_FOREIGN) or each macro giving access to a different struct, which then is used by qmlRegisterTypesAndRevisions to access the relevant parts of the actual class.