It's a bit of a pain that this will reject all cross-compiled snprintfs. Is there some way you can test for this at compile-time?
Does the nonstandard snprintf have exactly the same signature as the C99 snprintf? If not, we should be able to catch this at compile-time. Does the nonstandard implementation have a vsnprintf? If not, we could test for that at link-time and cross-compiles wouldn't have to substitute snprintf except on clearly pre-C99 systems. Basically, I'm looking for any way we can distinguish the nonstandard implementation without running it.
