EDIT: I've been getting a lot of down votes for this stance, surprisingly. Why not share your position if you don't agree? There must be a bunch of hardcore people on here who are writing directly on the metal in machine code. Short of that, you are in fact using someone else's code in all your projects.
I think that when most devs hear "using existing code", they're thinking of the latter, not the former.
What I'm saying is that calling a library/crate/whatever is an entirely different thing from using a tool like a compiler/IDE/etc. In the former, you're incorporating external code into your project. In the latter, you're not.
I think most people wouldn't say that you're "using someone else's code" in your project just by using a tool written by someone else because the tool's code is not being included in your project.
Perhaps I misunderstood you, though. Your statement "There must be a bunch of hardcore people on here who are writing directly on the metal in machine code" heavily implies that you believe that using an assembler or compiler counts as "using existing code". In this context, I don't think it does.
By the way, I do, in fact, sometimes write code directly in machine language. Not large amounts of it, of course, but some.
