Function safe_arch::floor_m128_s

#[must_use]pub fn floor_m128_s(a: m128, b: m128) -> m128

This is supported with target feature sse4.1 only.

Round the low lane of b toward negative infinity, other lanes a.

let a = m128::from_array([-0.1, 1.8, 5.0, 6.0]);
let b = m128::from_array([2.5, 3.0, 10.0, 20.0]);
assert_eq!(floor_m128_s(a, b).to_array(), [2.0, 1.8, 5.0, 6.0]);