If you think this needs more testing, do it yourself. The author of this project does not owe you any testing. If the Makefile works for author, that's good enough for the author. If it isn't good enough for you, fix it. The license allows you to do that. Then consider being nice and giving that fix back to the community with a pull request.
Don't come here on your high horse and post vile comments on something that is being shared with you as a gift! If you come here with your pull requests, code, or even better--your own projects, you would be welcome!
Some tips:
* Rather than call their way atrocious, try something like "Use $(CC) instead of hard coding gcc to avoid a lot of headaches down the road."
* Instead of:
>> "This also raises in me the suspicion that it hasn't been tested with no compiler other than GCC at whatever version the developer had installed on his machine, which is bad."
Consider:
"Test on other machines to make sure you don't depend on quirks of your local gcc installation."
Don't tear down. Build up.