atrace: include the binary in debug builds

This change makes the atrace module tag 'debug' so that the binary is
included in all debug builds.

Change-Id: I1fdb87be0461daf686e52ded04b37b9a122edea3
diff --git a/cmds/atrace/Android.mk b/cmds/atrace/Android.mk
index b6c55d4..c1a0d87 100644
--- a/cmds/atrace/Android.mk
+++ b/cmds/atrace/Android.mk
@@ -7,6 +7,6 @@
 
 LOCAL_MODULE:= atrace
 
-LOCAL_MODULE_TAGS:= optional
+LOCAL_MODULE_TAGS:= debug
 
 include $(BUILD_EXECUTABLE)