go get modernc.org/sqlite fails with ( //go:build comment without // +build comment )

I get this error:

go get modernc.org/sqlite
..\..\..\..\..\pkg\mod\modernc.org\libc@v1.14.11\mem.go:13:2: //go:build comment without // +build comment

The file looks fine to me? although i don't understand the contraints. But it clearly has both doesn't it?

$ head -n 20 ../../../../../pkg/mod/modernc.org/libc@v1.14.11/mem.go
// Copyright 2021 The Libc Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build !libc.membrk && !libc.memgrind
// +build !libc.membrk,!libc.memgrind

package libc // import "modernc.org/libc"

import (
        "modernc.org/libc/errno"
        "modernc.org/libc/sys/types"
        "modernc.org/memory"
)

I'm using go1.16.12 windows/amd64. It also happens with go1.16.6 darwin/amd64