patch for -Wno-long-long and early GNAT compilers

[Robert Dewar]

<<It would be easier for third parties to build from source if one or both
of those versions could be made to work.  Is this out of the question as
too difficult, or is it a more minor matter?  I'm not saying that this
should be a requirement, but I'd like some clue as to the cost.  Maybe
it's good enough that just 3.14 can do the job.
>>

I don't think anyone knows the cost here, I suspect that 3.13 may be reasonable
and may indeed work out of the box, but I doubt 3.12 is doable.

Generally we like to take advantage of new features to clean up and improve
code, but we make sure to do that one release behind. For example, the new
pragma Unreferenced is only available in 3.15, so we can't use it until 3.15
is generally released, but it would be much cleaner than the junk pragma 
Warnings (Off, ...) that we use now to suppress warnings.