CMake: Specify add_custom_command() dependencies
By specifying inputs and outputs for add_custom_command(), CMake will not rerun the steps every build.
Before:
[root@mkosi-682b1e787d39440f9053ab31fb8877a0 kservice]# ninja
[2/2] Running utility command for copy_menu
After:
[root@mkosi-682b1e787d39440f9053ab31fb8877a0 kservice]# ninja
ninja: no work to do.