Do not redefine math functions for floats if compiler complies with C99 or POSIX.1-2001

This is useful for gcc which does not define sqrtf/powf/... functions with preprocessor and therefore always used sqrt/pow/...
Float functions are generally 20-50% faster than their equivalents for double type.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54087 954f8c5b-7b00-dc11-b283-0030488c597c