rust.inc: include missing dependency on gcc-cross
rust.inc: include missing dependency on gcc-cross

-cross recipes do not automatically depend on gcc-cross, but rust
definitely needs it.

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