PATCH: Support x86_64 multilib on Solaris/x86 (PR ada/37681)

[Arnaud Charlet]

> I'm not sure: x86_64-linux doesn't use it (but other x86 specific modules),
> and the x86 code in g-bytswa-x86.adb should work just as well on x86_64.  I
> can of course also use the generic version, whatever you prefer.

Well, either you do test this package explicitely and we are sure, or we're
not sure, and we do not use it.

I'd prefer that you do as much testing as possible of course, otherwise
we end up with a half baked port which looks like it works, but does not
really in practice.

Also, stage3 is not the right stage for such new ports, so I'd rather we are
extra careful.

Arno