How exactly would that help in this situation? If both Rust and C have independent standard libraries loaded into the same process, each would have an independ

How exactly would that help in this situation? If both Rust and C have independent standard libraries loaded into the same process, each would have an independent set of environment variables. So setting a variable from Rust wouldn't make it visible to the C code, which would break the article's usecase of configuring OpenSSL. The only real solution is to have the operating system provide a thread-safe way of managing environment variables. Windows does so; but in Linux that's the job of libc, which refuses to provide thread-safety.