Add LOCAL_GROUP_STATIC_LIBRARIES

Set LOCAL_GROUP_STATIC_LIBRARIES := true to group the static libraries,
in case we need gcc flags "-Wl,--start-group" and "-Wl,--end-group" to
fix circular references.

Change-Id: I03c4901670112fcdd2bb0fe660b6924e5776fcf8
diff --git a/core/clear_vars.mk b/core/clear_vars.mk
index bc6ed0c..0469cb0 100644
--- a/core/clear_vars.mk
+++ b/core/clear_vars.mk
@@ -27,6 +27,8 @@
 LOCAL_PREBUILT_OBJ_FILES:=
 LOCAL_STATIC_JAVA_LIBRARIES:=
 LOCAL_STATIC_LIBRARIES:=
+# Group static libraries with "-Wl,--start-group" and "-Wl,--end-group" when linking.
+LOCAL_GROUP_STATIC_LIBRARIES:=
 LOCAL_WHOLE_STATIC_LIBRARIES:=
 LOCAL_SHARED_LIBRARIES:=
 LOCAL_IS_HOST_MODULE:=