cloudbuild: cross-compile to ARM no longer works
cloudbuild: cross-compile to ARM no longer works

The BUILD files for Rust dependencies that are generated by
`cargo raze` are specific to a particular configured `target`
architecture triple, in our case "x86_64-unknown-linux-gnu".

This means that cross-compiles don't work, in particular prost
and proc-macro fail to build.

project-oak/oak,project-oak/oak,project-oak/oak,project-oak/oak,project-oak/oak,project-oak/oak,project-oak/oak