Built in tracing should _not_ be run if it was not set on purpose. Warn as
loud as we can in order to inform the user that they are running a version
with tracing capabilities built in.

This commit also adds a subsys stub because utlimately the logging will happen
in the init phase but because the default log file is not set in the
sys_logging init function, the stub is not useful for now.

Signed-off-by: David Goulet <dgoulet@torproject.org>