Generated libcalls

[Martin v. Loewis]

> As IMO this is important for any freestanding target, I think we
> need something like -ffreestanding, telling gcc to *not* generate
> such libcalls but instead stop with an error in such cases.

Based on our previous discussion, I'd say this looks like the right
thing. 

There is an alternative interface to achieve the same effect, do I
dare say #pragma? :-)

Martin