RFR: 8369242: Rename URL variables in devkit/Tools.gmk

[Mikael Vidstedt]

Background (from JBS):

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.


Description:

The change renames the variables in question to include a `_URL` suffix and updates the uses accordingly.

Testing:

* Built devkit on linux-x64
* Verified that the JDK builds with the new devkit

-------------

Commit messages:
 - 8369242: Rename URL variables in devkit/Tools.gmk

Changes: https://git.openjdk.org/jdk/pull/27661/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27661&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369242
  Stats: 10 lines in 1 file changed: 0 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/27661.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27661/head:pull/27661

PR: https://git.openjdk.org/jdk/pull/27661