Environment variables Cargo sets for crates

[n1ght-hunter]

when building with cargo these env variables are injected for crates to use. https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates currently rust rules injects some of them if they exist. To work better with rust crates they all need injecting with an empty string unless the value is read from the cargo toml. many crates use the env!() macro to get these values and wont compile if they dont exist but are fine if they are an empty string