Just to be clear do you understand that all of these are built from source with documentation so you can recreate the binaries yourself?
As in it's completely source buildable with no unknown binaries. They just don't have a single 'build' that pulls all of these in and builds them at once. Instead you're following the build instructions for each part, creating libraries that you then link together at the end. This is due to the pain in the ass of cross-compiling Linux/Windows/UEFI binaries all in the one project. It's pretty reasonable.