[R] ISNAN() broken? in ver 2.x on MacOS X

[Bill Northcott]

I have a problem building an extension using ISNAN() on R version 2.0.x.

In R 1.9.1 Arith.h and Rmath.h contained code like

#ifdef IEEE_754
# define ISNAN(x) (isnan(x)!=0)
#else
# define ISNAN(x)      R_IsNaNorNA(x)
#endif
#define R_FINITE(x)    R_finite(x)
int R_IsNaNorNA(double);
int R_finite(double);

which works.

R 2.0.x has
# define ISNAN(x) (isnan(x)!=0)
unconditionally.

This breaks because on MacOS X in /usr/include/architecture/ppc/math.h 
isnan() is itself a macro thus:
#define      isnan( x )         ( ( sizeof ( x ) == sizeof(double) ) ?  
          \
                               __isnand ( x ) :                          
        \
                                 ( sizeof ( x ) == sizeof( float) ) ?    
         \
                               __isnanf ( x ) :                          
        \
                               __isnan  ( x ) )

This macro is not substituted because substitution is not recursive. So 
the build breaks with 'error: `isnan' undeclared'.

How can I fix this?

Bill Northcott