Converts benchmark JNI lib to NDK (*.mk) build to support older SDKs.

Bug: 120554763

Test: Ran com.android.nn.benchmark.app.NNTest on walleye-userdebug and blueline-userdebug
Change-Id: I837da0a56f1f1bc6270fc91b32ba26efd53fa90d
Merged-In: I837da0a56f1f1bc6270fc91b32ba26efd53fa90d
(cherry picked from commit d0b056f01bb9d53703d9b304791e38d39543ef2d)
diff --git a/Android.mk b/Android.mk
index 9b6402c..42dd1ad 100644
--- a/Android.mk
+++ b/Android.mk
@@ -26,7 +26,7 @@
 
 LOCAL_SRC_FILES := $(call all-java-files-under, src)
 LOCAL_PACKAGE_NAME := NeuralNetworksApiBenchmark
-LOCAL_JNI_SHARED_LIBRARIES := libnnbenchmark
+LOCAL_JNI_SHARED_LIBRARIES := libnnbenchmark_jni
 
 LOCAL_SDK_VERSION := 27
 LOCAL_ASSET_DIR := $(LOCAL_PATH)/../models/assets
@@ -37,3 +37,5 @@
 endif
 
 include $(BUILD_PACKAGE)
+
+include $(call all-makefiles-under,$(LOCAL_PATH))