... mmap() remains a system call to a C kernel designed for use from the C library in C programs, and you're running what amounts to an emulator.
The fact that you can imagine[1] an environment where that might not be the case doesn't mean that it isn't the case in the real world.
Your argument appears to be one of Personal Liberty: de facto truths don't matter because you can just make your own. This is sort of a software variant of a Sovereign Citizen, I think.
[1] Can you even link a "freestanding forth" with an mmap() binding on any Unix that doesn't live above the libc implementation? I mean, absent everything else it would have to open code all the flag constants, whose values change between systems. This appears to be a completely fictitious runtime you've invented, which if anything sits as evidence in my favor and not yours.
i'm not so much imagining an environment per se¹ as describing one i've already written, so i'm not entirely sure where any of this is coming from. if you care to have some additional assurance this isn't somehow an elaborate rhetorical trap, a previous comment about forth tail call elimination with a bit of demonstrative assembly is presumably only a short scroll down my profile. ctrl-f for cmov if you want to find it quickly. as i recall, it came up for similar reasons then because people often make similar incorrect generalizations about lots of things that implicitly sit atop a c runtime in their minds. that said, you're the first one to call me a sovcit before asking any clarifying questions so at least there's some new pizzazz there.
i was clear that i was talking specifically about linux precisely because this isn't something one can do portably for exactly the reasons you're describing (which, yes, makes porting things built like this off of linux before the point you've built up enough to be able to go through libc annoying and ad hoc at the very least).
the fact remains that i can, right now, non-theoretically, on a well supported common unixlike os, and entirely unrelated to whatever weird crusade you seem to have invented to stand in for my side of this discussion, link a pile of assembly with -static -nolibc, fire up the repl, and mmap files into memory as i please with nary a bit of c on the userspace side.
as i originally said, i'm happy to consider linux a weird exception to the point you're making in a wider context since this isn't something you can do portably, but there still are entirely useful things one can do today with mmap that involve zero userspace c code on a widely supported platform.
edit: lol forgot to even get to this part. i'm also somewhat curious what you mean with this bit: "you're running what amounts to an emulator." perhaps i'm not firing on all cylinders today but i fail to see how it's useful to characterize performing bare syscalls from assembly (or something more high-level built out of assembly legos) as an emulator in any way, but i'm open to having missed some interesting nuance there.
¹ unless you mean trivially (seeing as this is code i imagined and then proceeded to write) in which case i suppose i agree
Being able to declare dependencies that granular might actually be great for doing refactors and upgrades. Maybe we accepted too easily that dependencies for a project are global.