Build test-runner/tests

Previous change e254526f0fe5d22681555bd4a00b7ee96fee1dc1 inadvertently
removed the line to include the tests/Android.mk file.

(cherry picked from commit 006b7a2b760b89211b9530804118a8333cee314b)

Bug: 30188076
Test: make checkbuild
Change-Id: I59bd6ec5d317eb6306642974902e4c061e594aa8
Merged-In: Ia0ba14a70d2232d464420265a7a5f9c4dde3661b
diff --git a/test-runner/Android.mk b/test-runner/Android.mk
index 67f1354..706f636 100644
--- a/test-runner/Android.mk
+++ b/test-runner/Android.mk
@@ -116,3 +116,6 @@
 	$(hide) $(ACP) $(ANDROID_TEST_RUNNER_OUTPUT_REMOVED_API_FILE) $(ANDROID_TEST_RUNNER_REMOVED_API_FILE)
 
 endif  # not TARGET_BUILD_APPS not TARGET_BUILD_PDK=true
+
+# additionally, build unit tests in a separate .apk
+include $(call all-makefiles-under,$(LOCAL_PATH))