在编译的过程中会报出的错误，导致程序编译失败
Android NDK: Could not find application project directory !
Android NDK: Please define the NDK_PROJECT_PATH variable to point to it.
/Users/****/Downloads/android-ndk-r9c/build/core/build-local.mk:148: *** Android NDK: Aborting . Stop.
cd到jni目录后执行ndk-build