Prefix STRINGIFY with AOS_ for uniqueness.

A third party library collided.

Change-Id: Iaebafb4f5afc6967ea5923b51d678af5acda07a1
diff --git a/aos/util/log_interval.h b/aos/util/log_interval.h
index 54ebd6d..b6410a9 100644
--- a/aos/util/log_interval.h
+++ b/aos/util/log_interval.h
@@ -67,7 +67,7 @@
       : interval_(interval), level_(level), message_(message) {}
 
 #define AOS_LOG_INTERVAL(simple_log) \
-  simple_log.WantToLog(LOG_SOURCENAME ": " STRINGIFY(__LINE__))
+  simple_log.WantToLog(LOG_SOURCENAME ": " AOS_STRINGIFY(__LINE__))
   void WantToLog(const char *context) {
     context_ = context;
     interval_.WantToLog();