Your proprietary software won't be a derivative work of most of G++, but it will likely be a derivative work of libgcc (compiler runtime), libc (on Linux), and

Your proprietary software won't be a derivative work of most of G++, but it will likely be a derivative work of libgcc (compiler runtime), libc (on Linux), and libstdc++. Anyway, running copyrighted software without a valid license is clear cut unlawful, at least in the EU. That's because running the application requires copying it (into RAM). No, really, the law is that pedantic. "Loading" is a restricted act under Article 4 of the Computer Programs Directive.