Proposed resolution to aliasing issue.

[Daniel Berlin]

>
> The attribute might well be unnecessary, and once it's in it's in forever. 
> And I suspect supporting
> different semantics for different calls will create problems down the line, 
> somehow or other
> (although I confess I don't think of any offhand).

Attributes and flags have more or less the same effect from the POV of 
something like a call graph partitioner, (other stuff we'll hopefully have 
down the line).
It's just that now you have "incompatible" compilation units, instead of 
"incompatible" functions.

So there really isn't a good reason to have one and not the other, unless 
we believe we are going to screw up the smenatics :)