But this is not a de facto recursion limit of the system - the limit is encoded in the program itself, in the macros used to implement the limited recursion.
void f() { f(); } is only limited by the system, and if compiled on a system that automatically expands the stack to fill all available memory, you could in theory keep adding memory, and the system could handle more recursions. The recursion limit is external to the program.
But the linked c-preprocessor programs would have to be explicitly modified by adding more lines of code to achieve the same thing.
Yes, but as I point out elsewhere, Turing Completeness separates the expression from the machine. Machines will always have limits. But the expression of computation does not have to have limits.
Recursion depth limit is really a memory limit, so you just need someone to come and install more RAM when you run out in order to obtain de facto infinite memory, hence infinite recursion depth.
How is a "limit to how much memory [one] can address" not a physical, rather than logical, constraint?
Really, the crux of the matter is that you can have a function call itself an unbounded number of times in C (i.e. unbounded recursion). That you eventually run into a stack overflow is a limitation of the machine, not of the language; the definition of C does not prescribe a maximum number of recursive calls. This, together with conditionals, makes the C language Turing-complete.
That would break binary compatibility with all existing programs, though. So I guess the claim should be that it's impossible to implement a practically useful system without a de-facto recursion depth limit.
void f() { f(); } is only limited by the system, and if compiled on a system that automatically expands the stack to fill all available memory, you could in theory keep adding memory, and the system could handle more recursions. The recursion limit is external to the program.
But the linked c-preprocessor programs would have to be explicitly modified by adding more lines of code to achieve the same thing.