Function i16x8_relaxed_q15mulr

#[target_feature(enable = "relaxed-simd")]
pub fn i16x8_relaxed_q15mulr(a: v128, b: v128) -> v128

A relaxed version of i16x8_relaxed_q15mulr where if both lanes are i16::MIN then the result is either i16::MIN or i16::MAX.