Update Makefile to build OpenCL stub for ARM NN NNAPI HAL

The NNAPI HAL is using OpenCL which is provided by the libmali.
But libmali is exposed libOpenGL and not as libOpenCL.
This adds a stub OpenCL that is just used at build time to
build ARM NN. At runtime, this is libmali that will be used.

Signed-off-by: Alexandre Bailon <abailon@baylibre.com>

Android.mk

-# Android makefile
-# Build this using ndk as
-# ndk-build NDK_PROJECT_PATH=.  APP_BUILD_SCRIPT=Android.mk
-#
-
 LOCAL_PATH := $(call my-dir)
-
 include $(CLEAR_VARS)
 LOCAL_MODULE := libOpenCL
+LOCAL_MULTILIB := 64
 LOCAL_C_INCLUDES := $(LOCAL_PATH)/include/
 LOCAL_SRC_FILES :=  src/libopencl.c
-LOCAL_CFLAGS   = -fPIC -O2
-
-include $(BUILD_STATIC_LIBRARY)
-
+LOCAL_CFLAGS   = -fPIC -O2 -Wno-error
+LOCAL_UNINSTALLABLE_MODULE := true
+LOCAL_VENDOR_MODULE := true
+include $(BUILD_SHARED_LIBRARY)