With the change to our own configure logic for SASL, we seem to have missed the case where a "naked" --with-mongodb-sasl was provided. Unlike providing no option, this does not default to the default argument defined in the PHP_ARG_WITH (which is "auto"). This means that by passing just --with-mongodb-sasl we throw a warning that "yes" is not a supported value.

To correct this, we should interpret "yes" as "auto but warn if nothing is found".