Comment 11 for bug 737936

I think a debug_flag is the best way to go, because there is fairly
little risk of users or distributions unintentionally un/setting it
(as there is with -O), and it's also easy to specifically turn it on
if you want debug data from a user situation, or if you always want to
have it turned on yourself.

Our infrastructure there is certainly not perfect, and if you can
think of what in particular it's lacking do say so. One thing that
comes to mind is that I think we're a little unclear about how debug
flags should/can be used in testing, which might be good for
assertion-type checks.

(I guess possibly some tests would actually want to run scenarios of
debug on vs debug off.)