Even if not. Even the very first 8086 CPU had a tiny program in it. Only 512 21bit words long, but hey, it's still “a runtime”! Fully decoded and thoroughly explored, but… is it runtime already or not?
Ooh. That adds even more mud. You may say “if something is not part of the language but instead is implemented in the language” then it's not a runtime but mere library.
Okay. Well… what about Forth? Typically it's runtime is implemented in the language yet… not implemented in the language.
Because if you do that you would, of course, need full language to compile said runtime and then you would have a bootstrapping problem. Forth sidesteps that: since Forth compiler is so primitive the initial core is usually hand-compiled by humans!
Is it runtime because it was not, actually, produced from Forth sources or is it mere library since it was, actually, hand-compiled by human and thus undistinguishable from library code?