Update JikesRVM build file to fix classpath download

[qinsoon]

This PR updates JikesRVM to mmtk/jikesrvm#17. JikesRVM used to download classpath from ftp://ftp.gnu.org/gnu/classpath/classpath-0.99.tar.gz. However, recently we got this error:

get-classpath-from-web:
    [mkdir] Created dir: /home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/components/classpath/99p16
     [echo] Loading ftp://ftp.gnu.org/gnu/classpath/classpath-0.99.tar.gz into cache...
      [get] Getting: ftp://ftp.gnu.org/gnu/classpath/classpath-0.99.tar.gz
      [get] To: /home/runner/.buildit_components_cache/classpath-0.99.tar.gz
      [get] Error getting ftp://ftp.gnu.org/gnu/classpath/classpath-0.99.tar.gz to /home/runner/.buildit_components_cache/classpath-0.99.tar.gz

BUILD FAILED
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build.xml:313: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build.xml:318: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build/components/classpath.xml:298: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build/components/base.xml:70: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build/components/base.xml:76: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build/components/classpath.xml:72: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build/components/base.xml:87: The following error occurred while executing this line:
/home/runner/work/mmtk-core/mmtk-core/mmtk-jikesrvm/repos/jikesrvm/build/components/base.xml:98: java.io.IOException: sun.net.ftp.FtpProtocolException: Welcome message: 
	at sun.net.www.protocol.ftp.FtpURLConnection.connect(FtpURLConnection.java:325)
	at org.apache.tools.ant.taskdefs.Get$GetThread.openConnection(Get.java:778)
	at org.apache.tools.ant.taskdefs.Get$GetThread.get(Get.java:688)
	at org.apache.tools.ant.taskdefs.Get$GetThread.run(Get.java:[67](https://github.com/mmtk/mmtk-core/actions/runs/7526287919/job/20489328397?pr=1071#step:7:68)8)
Caused by: sun.net.ftp.FtpProtocolException: Welcome message: 
	at sun.net.ftp.impl.FtpClient.connect(FtpClient.java:1122)
	at sun.net.ftp.impl.FtpClient.connect(FtpClient.java:1105)
	at sun.net.www.protocol.ftp.FtpURLConnection.connect(FtpURLConnection.java:311)
	... 3 more

It seems gnu changed its FTP config, and it by default uses port 22 (SFTP) instead of port 21 (FTP). The JikesRVM PR specifies the port to 21.

[qinsoon]

We probably don't need this. The old build script seems working again: https://github.com/mmtk/mmtk-core/actions/runs/7526287919/job/20509342232?pr=1071