r13019: Again protect us against format string mismatches, with the new split

r13019: Again protect us against format string mismatches, with the new split
out proto headers.

The reason this is done in this way is that the attribute must be on
the prototype, not the actual function defintion.  Hence the macros
which expand to nothing in the C file, but expand to an __attribute__
in the prototype header.

Andrew Bartlett
(This used to be commit a88933668f908a398bb0d8bc7dc39c96cee40de6)