Use "[warning enabled by default]" for default warnings

[Robert Dewar]

On 2/9/2014 3:09 PM, Arnaud Charlet wrote:
>> IMO the natural assumption is that gnu++11 is enabled by default, which is
>> how Lars also read it.
>>
>> There seemed to be support for using "warning enabled by default" instead,
>> so this patch does that.  Tested on x86_64-linux-gnu.  OK to install?
>>
>> I'll post an Ada patch separately.
>
> FWIW this doesn't seem desirable to me, this will make the diagnostic longer.
> For Ada this wouldn't really disambiguate things, and some users may be
> dependent on the current format, so changing it isn't very friendly.
>
> Arno

can't we just reword the one warning where there is an ambiguity to 
avoid the confusion, rather than creating such an earthquake, which
as Arno says, really has zero advantages to Ada programmers, and clear
disadvantages .. to me [enabled by default] is already awfully long!