The correct approach is to build a custom cloud builder image that includes the required build tool. Cloud Build allows the use of custom Docker images for build steps, which ensures the necessary tools are available without relying on external downloads or bloating the repository. Option B is recommended as it's a best practice for including unavailable tools. Other options like downloading binaries (A) pose security and reliability risks, including binaries in the repository (C) is not ideal for version control, and filing a feature request (D) isn't a timely solution.