[Ada] Lock-free implementation of protected objects

[Arnaud Charlet]

> >> Looks good to me, go ahead, although I'm a bit surprised that you got an
> >> error,
> >> can you clarify what error you got?
> > 
> > IIRC, that the flag was undefined. 
> > If it's important I can revert the fix in my local tree and re-build.
> > Iaim

> No need to do that. Indeed, the flag must be defined for 
> all versions of system.ads.

No, as we agreed and discussed, the flag does NOT have to be defined for all
versions of system.ads, so this is a bug that needs to be fixed (precisely
for the issue raised here: we don't want unknown or new ports to be broken
by default).

> Please apply the patch, it 
> really seems to be just an oversight.

No, it's not just an oversight, and it's also not obvious as shown by this
discussion.

Arno