[Android] How to compile wpa_supplicant in AOSP

By the way, AOSP stands for Android Open Source Project,
http://source.android.com/

Once you follow the tutorial in AOSP, you can get the source of android platform, etc.
You can find various sources in external/ folder and if you want to compile, for instance wpa_supplicant, you can modify

You can change
WPA_BUILD_SUPPLICANT:=true in external/wpa_supplicant/Android.mk file

and try make in the top directory.