all: add go:build lines (#23468)

Generated by go1.17 fmt ./...

crypto/blake2b/blake2bAVX2_amd64.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.7 && amd64 && !gccgo && !appengine
 // +build go1.7,amd64,!gccgo,!appengine
 
 package blake2b

crypto/blake2b/blake2b_amd64.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !go1.7 && amd64 && !gccgo && !appengine
 // +build !go1.7,amd64,!gccgo,!appengine
 
 package blake2b

crypto/blake2b/blake2b_f_fuzz.go

@@ -1,3 +1,4 @@
+//go:build gofuzz
 // +build gofuzz
 
 package blake2b

crypto/blake2b/blake2b_ref.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build !amd64 || appengine || gccgo
 // +build !amd64 appengine gccgo
 
 package blake2b

crypto/blake2b/register.go

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.9
 // +build go1.9
 
 package blake2b