As far as I know gcc doesn't turn warnings into errors from one release to another. In fact the default is that no warning is considered an error, unless you use options to force a different behavior. This is something that Apple seems to do (last time I used a mac I've seen that the Apple compiler that is a proprietary build of clang have some warning considered errors enabled by default), but I never seen in any Linux distribution.
For code, you can compile by specifying the correct C standard. Unless the build system is badly written and doesn't add the correct -std=cXY to gcc of course (but it's trivial to fix).
Regarding libraries, that is a real problem. Because to compile and old software you should use old version of the libraries, and they are usually not easy to get (and then it's a pain to compile them, and put the correct environment variables to make the software you are building link to that libraries and not the one in the system).
I'm always able to compile a software, even an old one, on my system, and it never took me more than a couple of minutes. But I recognize that I'm a pretty experienced Linux user, so sure for the average user having a binary package is more easy.