Update rtems-source-builder to use new GitLab Repo

[arielswalker]

The three RTEMS containers downloads rtems-source-builder from GitHub which downloads additional packages such as automake from links that no longer exist. When visiting the links it states " We have migrated to GitLab please see https://gitlab.rtems.org/groups/rtems/". The three containers should use the new repository from GitLab instead of GitHub.

Example of error: downloading https://git.rtems.org/rtems-tools/plain/tools/4.11/automake/automake-1.12.6-bugzilla.redhat.com-1239379.diff?h=4.11: all paths have failed, giving up