RTG-1339 Support post-quantum hybrid key exchange

Func spec: https://wiki.cfops.it/x/ZcBKHw

vendor/github.com/cloudflare/circl/internal/sha3/xor.go

@@ -0,0 +1,15 @@
+// Copyright 2015 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 (!amd64 && !386 && !ppc64le) || appengine
+// +build !amd64,!386,!ppc64le appengine
+
+package sha3
+
+// A storageBuf is an aligned array of maxRate bytes.
+type storageBuf [maxRate]byte
+
+func (b *storageBuf) asBytes() *[maxRate]byte {
+	return (*[maxRate]byte)(b)
+}