Fix hello world binary so that it does something useful by default #630

Job	Run time
build_attest_all (buildconfigs/key_xor_test_app.sh)	17m 49s
build_attest_all (buildconfigs/oak_client_android_app.sh)	51m 49s
build_attest_all (buildconfigs/oak_containers_agent.sh)	10m 58s
build_attest_all (buildconfigs/oak_containers_kernel.sh)	30m 51s
build_attest_all (buildconfigs/oak_containers_orchestrator.sh)	24m 15s
build_attest_all (buildconfigs/oak_containers_stage1.sh)	22m 58s
build_attest_all (buildconfigs/oak_containers_syslogd.sh)	23m 16s
build_attest_all (buildconfigs/oak_containers_system_image.sh)	25m 56s
build_attest_all (buildconfigs/oak_containers_nvidia_system_image.sh)	29m 44s
build_attest_all (buildconfigs/oak_echo_enclave_app.sh)	16m 47s
build_attest_all (buildconfigs/oak_echo_raw_enclave_app.sh)	16m 47s
build_attest_all (buildconfigs/oak_functions_enclave_app.sh)	16m 12s
build_attest_all (buildconfigs/oak_functions_insecure_enclave_app.sh)	17m 23s
build_attest_all (buildconfigs/oak_orchestrator.sh)	18m 20s
build_attest_all (buildconfigs/oak_restricted_kernel_simple_io_init_rd_wrapper_bin.sh)	43m 36s
build_attest_all (buildconfigs/stage0_bin.sh)	42m 28s
build_attest_all (buildconfigs/stage0_bin_tdx.sh)	42m 13s
	7h 31m 22s

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