@Guillaume Chauvel has posted a solution :
https://sourceforge.net/p/launch4j/discussion/332683/thread/a988649580/

1 - Get Launch4j 3.12 source (https://sourceforge.net/p/launch4j/git/)
2 - Patch Builder.java to add '.add("--no-insert-timestamp")' option to 'ld'
3 - Update bin\bin-win32\ld.exe (and bin\bin-win32\windres.exe) with https://osdn.net/projects/mingw/releases/70619 (binutils-2.32-1-mingw32-bin*) (I am running launch4j on Windows)