vendor: Update everything

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4620

vendor/golang.org/x/crypto/salsa20/salsa/salsa2020_amd64.s

@@ -5,7 +5,7 @@
 // +build amd64,!appengine,!gccgo
 
 // This code was translated into a form compatible with 6a from the public
-// domain sources in SUPERCOP: http://bench.cr.yp.to/supercop.html
+// domain sources in SUPERCOP: https://bench.cr.yp.to/supercop.html
 
 // func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
 // This needs up to 64 bytes at 360(SP); hence the non-obvious frame size.

vendor/golang.org/x/crypto/salsa20/salsa/salsa20_amd64.go

@@ -13,11 +13,12 @@ package salsa
 func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	if len(in) == 0 {
 		return
 	}
+	_ = out[len(in)-1]
 	salsa2020XORKeyStream(&out[0], &in[0], uint64(len(in)), &counter[0], &key[0])
 }

vendor/golang.org/x/crypto/salsa20/salsa/salsa20_ref.go

@@ -203,7 +203,7 @@ func core(out *[64]byte, in *[16]byte, k *[32]byte, c *[16]byte) {
 }
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	var block [64]byte