GitLab is used only for code review, issue tracking and project management. Canonical locations for source code are still https://gitweb.torproject.org/ https://git.torproject.org/ and git-rw.torproject.org.
Over the years we have accumulated binary blobs in the source code/toolchains we take for building Tor Browser. This is the parent ticket to track those issues.
Note: this ticket is not concerned with the toolchains/packages that come with the OS we use for building.