I got a bit further, just by including stdlib.h.
But, now I’m getting complaints about a number constant in math.h, M_PI.
Somehow it is not defined, so I am getting an error about it in atone.cpp (even though it includes math.h).
The #define's in my math.h are wrapped in some conditions #if defined __USE_MISC || defined __USE_XOPEN, I’m asuming those are not true for some reason. 
This is getting to be kind of kludgy build, I guess I will just have to define them in the module headers then…