Add vendor to improve building speed.

This also adds ability to be built in network-constrained environment.

vendor/golang.org/x/crypto/sha3/keccakf_amd64.go

@@ -0,0 +1,13 @@
+// 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 && !purego && gc
+
+package sha3
+
+// This function is implemented in keccakf_amd64.s.
+
+//go:noescape
+
+func keccakF1600(a *[25]uint64)