"Q2a 1.7.5 is broken for php 5.3 and 7.0" -> This is absolutely false
Firstly, Q2A works perfectly fine in any PHP 5.2+ version. In the latest PHP versions (I think this started happening on 7.1) you'd get a few notices or warnings that can absolutely be ignored or even manually fixed by changing just a few lines (they can be taken from the fixes in the 1.8 or dev branch in the repo)
Secondly, you've linked to a build of a repository that is not the official Q2A repository. Here are the builds for Q2A:
https://travis-ci.org/q2a/question2answer/builds and, in particular for v1.7.5, this one:
https://github.com/travis-ci/travis-ci/issues/2963
Thirdly, the fact that a build fails doesn't mean Q2A doesn't work or that it is broken. It just means the build failed. Understanding why that happened should lead (or not) to that conclusion. In fact, if you see the link I provided it failed, but the reason is absolutely unrelated to Q2A: "The command "phpenv global 5.3" failed and exited with 1 during". This issue happens because PHP support for 5.3 on Ubuntu Trusty is dropped (you can see here:
https://github.com/travis-ci/travis-ci/issues/2963).
In conclusion: it works perfectly fine up to 7.0 and you get a few notices/warnings in your web server log if you use 7.1+ and that's it