What is peculiar about our math.h implementation?

I'm trying to compile LDC (D compiler for LLVM), I fixed most errors, but this one puzzles me: /home/petr/sources/ldc/dmd2/root/port.c: In static member function 'static int Port::isNan(double)': /home/petr/sources/ldc/dmd2/root/port.c:382: error: '::isnan' has not been declared

Re: What is peculiar about our math.h implementation?

I'm trying to compile LDC (D compiler for LLVM), I fixed most errors, but this one puzzles me: /home/petr/sources/ldc/dmd2/root/port.c: In static member function 'static int Port::isNan(double)': /home/petr/sources/ldc/dmd2/root/port.c:382: error: '::isnan' has not been declared