LAKITU: allow usage of cargo.eclass in non-rust packages

Export CARGO_HOME in cargo_gen_config so it can be picked up
by the cargo invocation outside of the cargo.eclass (i.e. by
setuptools-rust python module)

BUG=b/257113269
TEST=presubmit
RELEASE_NOTE=None

Change-Id: I3a70db14158f5f4cbcd6f9fb71247c32e8779c16
Reviewed-on: https://cos-review.googlesource.com/c/third_party/overlays/chromiumos-overlay/+/42647
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
1 file changed