Well, the touch command is also available on Linux. So I use the following lines now in my script that creates a new system image to force pre-compilation of the user modules:
cd src
touch *.jl # make sure all modules get recompiled in the next step
cd ..
julia --project -J MakieSys.so -e "push!(LOAD_PATH,joinpath(pwd(),\"src\"));using Utils, KCU_Sim, KPS3, Plot2D, RTSim"
This should also work on git-bash which I use on Windows.