how to build android_external_openvpn_ics with ndk-build

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http://stackoverflow.com – everyone There is a project on github --> https://github.com/CyanogenMod/android_external_openvpn/tree/ics ,After download the sourcecode , I just want to build it use NDK-BUILD command in Linux(Centos 6.3) , But the author does not say anything about it ; So, I just ndk-build it ( I have test ndk-build is ok ) , it shows : Android NDK: Could not find application project directory ! Android NDK: Please define the NDK_PROJECT_PATH variable to point to it. what may cause this warning ? & how can I build it ,TKS ! (HowTos)