Defining a HAVE_J0 in config.h for gfortran?

[Steve Kargl]

I'm contemplating adding j0, j0f, j1, j1f, y0, y0f, y1, and y1f
intrinsic functions to gfortran for compatibility with g77.  In
gcc/libgfortran I can modify configure.ac with a line similar to

AC_CHECK_LIB([m],[j0],[AC_DEFINE([HAVE_J0],[1],[libm includes j0])])

to check that j0 is present in libm.  I however need the HAVE_J0
symbol in gcc/gcc/fortran.  There is no configure.ac in this 
directory, so I need some other way to define HAVE_J0.  Any pointers
would be appreciate.

-- 
Steve