third_party: Add the libsync library from Android

third_party/libsync/include/sw_sync.h

Index: third_party/libsync/include/sw_sync.h
diff --git a/third_party/libsync/include/sw_sync.h b/third_party/libsync/include/sw_sync.h
new file mode 100644
index 0000000000000000000000000000000000000000..fda1c4c57c0cd9fb6fea08c1310a16817b7fc65a
--- /dev/null
+++ b/third_party/libsync/include/sw_sync.h
@@ -0,0 +1,35 @@
+/*
+ *  sw_sync.h
+ *
+ *   Copyright 2013 Google, Inc
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef __SYS_CORE_SW_SYNC_H
+#define __SYS_CORE_SW_SYNC_H
+
+__BEGIN_DECLS
+
+/*
+ * sw_sync is mainly intended for testing and should not be compiled into
+ * production kernels
+ */
+
+int sw_sync_timeline_create(void);
+int sw_sync_timeline_inc(int fd, unsigned count);
+int sw_sync_fence_create(int fd, const char *name, unsigned value);
+
+__END_DECLS
+
+#endif /* __SYS_CORE_SW_SYNC_H */