It started off there, but I wasn't quite sure.

At the moment eclrtl and bcd are independent.  In the end that's why it was added to platform.h.

I could move it back to eclrtl.hpp and add an include dependency of bcd on eclrt.
Alternatively I could move the bcd wrapper functions into eclrtl, keep the divide by zero logic in eclrtl, and have eclrtl dependent on bcd.  

That might be the cleanest in the long term (e.g., if we were to switch to using a 3rd party bcd library).