Update dependencies (#333)

vendor/modernc.org/libc/sync.go

@@ -0,0 +1,17 @@
+// Copyright 2021 The Libc Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package libc // import "modernc.org/libc"
+
+import (
+	"sync/atomic"
+)
+
+var __sync_synchronize_dummy int32
+
+// __sync_synchronize();
+func X__sync_synchronize(t *TLS) {
+	// Attempt to implement a full memory barrier without assembler.
+	atomic.StoreInt32(&__sync_synchronize_dummy, atomic.LoadInt32(&__sync_synchronize_dummy)+1)
+}