func Sum(out *[16]byte, m []byte, key *[32]byte) {
	if cpu.S390X.HasVX {
		var mPtr *byte
		if len(m) > 0 {
			mPtr = &m[0]
		}
		if cpu.S390X.HasVXE && len(m) > 256 {
			poly1305vmsl(out, mPtr, uint64(len(m)), key)
		} else {
			poly1305vx(out, mPtr, uint64(len(m)), key)
		}
	} else {
		sumGeneric(out, m, key)
	}
}
Sum generates an authenticator for m using a one-time key and puts the
16-byte result into out. Authenticating two different messages with the same
key allows an attacker to forge messages at will.
package poly1305
import (
	"golang.org/x/sys/cpu"
)
func poly1305vx(out *[16]byte, m *byte, mlen uint64, key *[32]byte)
func poly1305vmsl(out *[16]byte, m *byte, mlen uint64, key *[32]byte)