Toward generic atomic operations

Good points. The intention here is not to advocate for "proprietary extensions", but on some level I'm saying that if a project relies upon GCC, it's worth just considering using their existing atomics rather than re-implementing the wheel with inline assembly. An preferred alternative is to use an existing library, but that is not always possible. I just reviewed some of the Fedora ARM codebase for inline assembly and this kind of stuff showed up way more than I expected. It's something that needs fixing. I hope C11 is quickly adopted as means to do so.