add vendoring

vendor/golang.org/x/crypto/chacha20/chacha_noasm.go

@@ -0,0 +1,14 @@
+// Copyright 2018 The Go 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 (!arm64 && !s390x && !ppc64le) || (arm64 && !go1.11) || !gc || purego
+// +build !arm64,!s390x,!ppc64le arm64,!go1.11 !gc purego
+
+package chacha20
+
+const bufSize = blockSize
+
+func (s *Cipher) xorKeyStreamBlocks(dst, src []byte) {
+	s.xorKeyStreamBlocksGeneric(dst, src)
+}