math: implement most of glibc's __*_finite functions
These are supposed to be specialisations for speed, but these are just faked. Some warnings were added too, if they return infinite values. As a side effect of this change, scalbl is also now implemented. As noted, not all functions are implemented; the big two blockers are an implementation of j0l and y0l; I imagine Bessel functions aren't too widely used, so I doubt that many things will want them. Someone (not it) can implement them later.