lang/rust: Make OpenSSL use the system default truststore in Cargo

[michaelo]

Summary

Cargo uses curl-rust and git2-rs (which uses curl-rest as well).
Unfortunately, git2-rs calls openssl_probe::init_ssl_cert_env_vars()
unconditionally which breaks the process environment by setting an invalid
value for SSL_CERT_DIR and then the system default truststore is circumvented,
resulting in certificate validation errors even if certlctl(8) manages
everything nicely.

Upstream issues:

• https://github.com/alexcrichton/openssl-probe/issues/37
• https://github.com/rust-lang/git2-rs/pull/1130

[michaelo]

Rust maintainers, please have a look. This is quite annoying issue especially because it is hard to diagnose from a high level perspective.

[michaelo]

Hope to remove patch when upstream accepts it.

[michaelo]

Mentors, any opinion?