[PATCH v2] include: Add some math function declarations.

[Piotr Caban]

Hi Daniel,

On 02/07/18 19:58, Daniel Lehman wrote:
> static inline int isnan( double x ) { return _isnan( x ); }
_isnan is not defined now. It will cause warnings when mshvcrt.h is used 
without float.h header.

Thanks,
Piotr