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 :)
