The file libmodules.android.debug.armv7.neon.a appears only when you build the godot engine not the project.
If you want to add some custom modules to the engine you should build the export templates. For example in order to build android templates I do these commands:
cd <path to godot engine>
scons platform=android target=release android_stl=yes verbose=yes
After that I copy godot/bin/android_release.apk to ~/.godot/templates/
And then I export my project with new functionality.