Don't use -ffast-math functions for libc compatibility implementation, since
then the function ends up calling itself. This may not be ideal for performance
but should be insignificant in practice.
On Linux, precompiled libraries may be made with a glibc version that is
incompatible with the system libraries that Blender is built on. To solve
this we add a few -ffast-math symbols that can be missing.
Differential Revision: https://developer.blender.org/D6930
Brecht Van Lommel