undefined symbol: _fxstat when using NAG FORTRAN with potato (only)

["David Gaudine" <david@annette.concordia.ca>]

I have an application that runs fine on hamm and slink, but on potato
it says
   undefined symbol: _fstat

The application was compiled with NAG FORTRAN 95, and the
symbol is referenced by a shared library that was provided
with the compiler.  I've verified that _fstat is a system routine
of some sort, not a NAG routine.  Does anyone know more specifically
where it comes from, and in what way it has changed between slink
and potato?  (If indeed it has changed; I may just not be able to
link with it.)
After looking at some web pages that are way over
my head, all I could determine is that it has something to do with
gcc and/or libc6.

I've reported my problem to NAG, but I expect better results here
because it's Linux that's changed recently, not the compiler.