go: x/arch/x86/x86asm: missing instructions: FLDZ, FLDLN2

package main

import "golang.org/x/arch/x86/x86asm"

func main() {
	text := []byte{0xd9, 0xee} // fldz
	_, err := x86asm.Decode(text[:], 64)
	if err != nil {
		panic(err)
	}
}

I found two missing instructions (they’re also missing in x86.csv, which suggests that x86.csv is not complete): 0xd9 0xed: FLDLN2 0xd9 0xee: FLDZ

There are also some missing AVX instructions: e.g. c4 c1 f3 2a cc vcvtsi2sd %r12,%xmm1,%xmm1

/cc @rsc