rcc embeds time in output

When building packages on openSUSE twice, I found that results always differed for ~15 packages:

umbrello syntax-highlighting wireshark qmmp spectator qbittorrent bitcoin libqt5-qtwebkit gpxsee boomaga gammaray mathgl goldendict gcompris-qt breeze5-icons

See https://reproducible-builds.org/ for why this matters.

This is because src/tools/rcc/rcc.cpp has RCCFileInfo::writeDataInfo that calls lastModified.toMSecsSinceEpoch

and input files are generated during build, and thus carry the build time.

e.g. umbrello-17.04.2/umbrello/CMakeLists.txt has

configure_file(umbrelloui.rc.cmake ${CMAKE_CURRENT_BINARY_DIR}/umbrelloui.rc @ONLY)

I tested that the attached simple patch helps, but for a proper fix, we probably want to clamp timestamps to be lower or equal to SOURCE_DATE_EPOCH similar to

https://github.com/rpm-software-management/rpm/pull/144

https://github.com/michaelrsweet/mxml/commit/b79d3e0f07495b4a113f1ad95ae08c19664ea5ac