Don't hard-code a target family of Unix

[Ericson2314]

Rust target specs actually support multiple target families, where just one needs to match, so we do too.

Reverse the order of the comparison so it is more consistent: wanted before the target's single value or list.

[Ericson2314]

The new logic should be backported into a toTargetFamilies next to the others in the "rust lib". Then this is ready to be merged.

[Ericson2314]

(The tests passed locally)