isfinite() on Linux

[Ralph Lange <ralph.lange@gmx.de>]

All,

Working on a patch for Base I am having trouble trying to use isfinite() 
on Linux (gcc 4.9.0) - isinf() and isnan() work fine, but isfinite() 
gets me an "implicit declaration" warning and a missing symbol when linking.
Any ideas? All these macros should be POSIX and defined in math.h, right?

Thanks a lot,
~Ralph