Bug 574684 - Update JDT and Platform porting guide links for 4.21 in Welcome page Change-Id: Ic4648878e4324bd6e6864026c58a8cb2738a1569 Signed-off-by: Roland Grunberg <rgrunber@redhat.com> Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt/+/182994 Tested-by: JDT Bot <jdt-bot@eclipse.org>