Replace QDateTime::to_Time_t/from_Time_t with to/fromSecsSinceEpoch
Summary:
QDateTime::toSecsSinceEpoch obsoletes to_Time_t, likewise for from_Time_t.
Both functions are available since Qt 5.8.
Reviewers: Frameworks, apol
Reviewed By: apol
Subscribers: kde-frameworks-devel
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D20162