I thought of that too but didn't think I cared. We don't have an
existing header that seems appropriate. Since it's an __ function,
it shouldn't really be declared in a "user" header. So I guess it
would be some new header like<bits/fortify.h>. But then libstdc++
would require a new-enough libc to have that header. If this is
only going to be called from the library itself that doesn't seem
like a problem since it can just autoconf it. But if Florian
intends to call it from libstdc++ header files (e.g. template code)
then it could be an issue.