VFPU: Ensure that sin(4*x) returns 0.0 (and cos 1) for all x. Fixes #2921

This also makes it easier to replace our VFPU sin/cos implementations with some approximation later.

Note that our sinf/cosf function replacements should not call these, they are expected to behave like libc sinf/cosf, I would think.

Fixes #2921
Hmm, not sure this is rounding right?

Angle 1 = 1*pi/2 = sin=1,cos=0
Angle 2 = 2*pi/2 = sin=0,cos=-1
Angle 3 = 3*pi/2 = sin=-1,vos=0
Angle 4 = 4*pi/2 = sin=0,cos=1

However, `3 - floor(3 * 4) * 0.25` = `3 - 12 * 0.25` = `0`.

-[Unknown]