Check Rust dep is a Module before checking target.

The Target checks against the os type and arch type occur before we
determine a dependency is a rust.Module / cc.Module. This meant
rust_defaults would fail this check, preventing them from being used.

Bug: 140963307
Test: make a rust_binary_host using rust_defaults.
Change-Id: Ibf43635f14ad367b4ce8016a2196f8c645b36bfe