add an implementation of memory transactions + tests

Change-Id: Id901328da7d246268b7af951729acb1fada06836
diff --git a/aos/common/util/BUILD b/aos/common/util/BUILD
index 646f3bf..bd70463 100644
--- a/aos/common/util/BUILD
+++ b/aos/common/util/BUILD
@@ -172,3 +172,10 @@
     '//aos/testing:googletest',
   ],
 )
+
+cc_library(
+  name = 'compiler_memory_barrier',
+  hdrs = [
+    'compiler_memory_barrier.h',
+  ],
+)