If you're within the terms of the license, you're fine. The developer should say so in the license (or choose another license) if they don't want it reproduced

If you're within the terms of the license, you're fine. The developer should say so in the license (or choose another license) if they don't want it reproduced anywhere. A link to the original is common courtesy, however. In the case of the C compiler, I think the modifications are under the same license as the original, but I'm not totally certain. If they aren't it would be cause for concern.