Build TestablesTests as part of top-level make

Necessary for postsubmit to work.

Test: make -j48 TestablesTests
Change-Id: Ifaeed98681621cf6a4a9d580cd3e0096ad98bb67
diff --git a/tests/testables/Android.mk b/tests/testables/Android.mk
index 759bc35..0e36981 100644
--- a/tests/testables/Android.mk
+++ b/tests/testables/Android.mk
@@ -31,3 +31,5 @@
 LOCAL_JAVA_LIBRARIES := android.test.runner
 
 include $(BUILD_STATIC_JAVA_LIBRARY)
+
+include $(call all-makefiles-under,$(LOCAL_PATH))