This function projects a point in the plane onto the surface of a
Riemann Sphere, the one-point compactification of the complex plane.
Each finite point
Every complex infinite value is projected to a single infinite value,
namely to positive infinity on the real axis.
These functions first appeared in glibc in version 2.1.
In glibc 2.11 and earlier, the implementation does something different
(a stereographic projection onto a Riemann Sphere).