NotFound, message: "No such file or directory"

[NikZak]

Launching it this way
WITNESS_CPP=[absolute path to my circom circuit] cargo build --release

build.rs has this

fn main() {
    witness::generate::build_witness()
}

However, I get

called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }

Any hint why this may be happenning? Am I using the correct system variable?

[NikZak]

Should follow build.rs in this repo