Now that we have a means of providing data about the toolchain to clients, we can set up the server build to run against the toolchain release configured for the platform. In cases where the required toolchain is not present, the build should look for "latest" path at /opt/mongodbtoolchain/<version> and fail if a toolchain is not found there, or emit a warning and use it. (This last part preserves the behavior for local developer builds and allows us to migrate Evergreen away from the path.)