To keep us on our toes the source bundle URL variables in Tools.gmk are simply named after the corresponding dependency. For example (from Tools.gmk):

GCC := http://ftp.gnu.org/pub/gnu/gcc/$(gcc_ver)/$(gcc_ver).tar.xz

There's also a lower case variable set up for the "done" marker file for each dependency (from Tools.gmk):

# Define marker files for each source package to be compiled
$(foreach dep,$(dependencies),$(eval $(dep) = $(TARGETDIR)/$($(dep)_ver).done))

Will do something equivalent to:

gcc = target/dir/gcc-14.2.0.done


Let's rename the former variable to make it clearer that is, in fact, a URL.