If you are looking at some repository for Ubuntu's source code, and find that their build process isn't perfectly documented as regards the version of gcc they

If you are looking at some repository for Ubuntu's source code, and find that their build process isn't perfectly documented as regards the version of gcc they use, that really isn't a GPL violation no matter how hard you try to claim that it is. You don't have a moral right to base a distribution on binaries produced by some other distribution. Unless you are going to produce actual evidence of a legal violation you really don't have anything here.