Avoid indeterminism in kcolorschemeeditor
Without this patch,
build/kcms/colors/CMakeFiles/kcolorschemeeditor.dir/kcolorschemeeditor_autogen/mocs_compilation.cpp.o
and the resulting /usr/bin/kcolorschemeeditor varied from parallelism.
See https://reproducible-builds.org/ for why this matters.
See also https://bugzilla.opensuse.org/show_bug.cgi?id=1109420