Which cocos2d-x version are you using? Seems like you didn't define your env variables correctly. Please have a look at this tutorial and make sure you define the following variables:
- COCOS2DX_ROOT : should point to the root directory of cocos2d-x
- ANDROID_SDK_ROOT : Should point to the root directory of the Android SDK
- NDK_ROOT : Should point the to root directory of the Android NDK
- NDK_TOOLCHAIN_VERSION : Which Android NDK toolchain should be used