Convert go_binary linkstamp to x_defs

hack/print-workspace-status.sh

@@ -29,6 +29,8 @@ kube::version::get_version_vars
 # instead of volatile-status.txt.
 # Stamped rules will be retriggered by changes to stable-status.txt, but not by
 # changes to volatile-status.txt.
+# IMPORTANT: the camelCase vars should match the lists in hack/lib/version.sh
+# and pkg/version/def.bzl.
 cat <<EOF
 STABLE_BUILD_GIT_COMMIT ${KUBE_GIT_COMMIT-}
 STABLE_BUILD_SCM_STATUS ${KUBE_GIT_TREE_STATE-}