Of course C relies on an OS. The point of an OS is securely mediating access to resources; a C program is going through the OS, using syscalls, in order to do stuff like 'write a file'. Which bears a certain resemblance to what this code is doing...
Let me repeat myself -- "you don't have to". C runs well on bare metal, that's why most bootloaders, kernels and low level drivers use it. Of course, you can make as many dependencies as you wish, but unlike high level languages, C doesn't rely on OS for it's core features.
