add more warnings to the JNI build

java/jni/Application.mk

@@ -1,3 +1,3 @@
 APP_ABI := armeabi armeabi-v7a arm64-v8a x86
 APP_STL := gnustl_static
-APP_CPPFLAGS += -fexceptions
+APP_CPPFLAGS += -Wall -fPIE -fstack-protector -fexceptions