- Only copy over branding files if they are newer
Typically I have KDevelop open while working on Calamares; if I
am editing settings in `branding.desc` in the build directory,
then every time KDevelop runs CMake in the background, my
changes (for testing branding things!) would be overwritten.
Don't do that.
For normal builds with a clean build directory, this doesn't change
anything since the target is missing; changing a file in the
source directory **will** copy it over the build directory version.