Since there were no objections, updated Qt version.
cmake, compile and run
QOverload is only available in Qt >= 5.7, and Qt 5.9 is the earliest supported version.
See also https://bugs.kde.org/show_bug.cgi?id=405212 .
I proposed this change in the discussion of D19623 and there were no objections for a month.
After rethinking this, I agree with you, Nikita. We should not impose the burden of supporting an outdated Qt version on ourself.
Please also close https://bugs.kde.org/show_bug.cgi?id=405212 when merging this.
Thank you, Yuri and Alex!