Mark objects death at end of scope

[Eric Botcazou]

> There is a bug about not using -fexceptions (50857).

Then let's fix it, as you said there "We fail to pass -fno-exceptions -fno-rtti 
to g++ for stage2 and stage3 building the host binaries.  That leads to 
increased compile-time and possibly runtime."  And now that will be worse.

> If gnattools are built with the C++ compiler they should also link with the
> G++ driver, so that's  worth fixing anyway I think.

gnattools is built with the C compiler, but it reuses a couple of object files 
of libbackend.a that are now compiled with C++.

-- 
Eric Botcazou