If you have INT_MIN along with any other negative number in the array then your program has undefined behavior in C. Signed integer overflow is UB (but unsigned overflow is not).
What? Why? There’s no addition needed to solve this problem. The example implementation does invert each element, which is undefined for INT_MIN, but it would be trivial to just skip INT_MIN elements (since their additive inverse is never in the set).
Rust is only a little better. With default settings, it will panic if isize::MIN is in the input slice in a debug build, and in a release build will incorrectly return true if there are two such values in the input. But in C you'll get unicorns and rainbows.
But in formally verified C you’ll have the algorithm that’s correct for that type (skip INT_MIN), or you won’t have a proof.