Fix Android builds using cmake 3.12.1

Summary: Only extract the the stl shared object without the rest of libraries.

Test Plan: Built gcompris

Reviewers: Frameworks, vkrause

Reviewed By: vkrause

Subscribers: kde-frameworks-devel, kde-buildsystem

Tags: Frameworks, Build System

Differential Revision: https://phabricator.kde.org/D15685