include: cleanup for -Wsystem-header

- warnings as errors, or errors introduced when -Wsystem-header
  was experimentally introduced.

Change-Id: Ia8f5b3c1c1096e191741223d52526aa48c7f1cc4
diff --git a/include/cutils/trace.h b/include/cutils/trace.h
index dbd5e25..3f49e8c 100644
--- a/include/cutils/trace.h
+++ b/include/cutils/trace.h
@@ -20,6 +20,7 @@
 #include <inttypes.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <sys/cdefs.h>
 #include <sys/types.h>
 #include <unistd.h>