rust-cross: fix build where TARGET_ARCH and HOST_ARCH are the same
rust-cross: fix build where TARGET_ARCH and HOST_ARCH are the same

By copying exactly the target we intend to.

Fixes #77

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