rust: avoid using flags for TARGET for non-TARGET
rust: avoid using flags for TARGET for non-TARGET

meta-rust/meta-rust,cardoe/meta-rust,cardoe/meta-rust,meta-rust/meta-rust,meta-rust/meta-rust,cardoe/meta-rust,meta-rust/meta-rust,starlab-io/meta-rust,jmesmon/meta-rust,jmesmon/meta-rust,jmesmon/meta-rust,starlab-io/meta-rust,meta-rust/meta-rust,jmesmon/meta-rust,cardoe/meta-rust