Since Bintray is (soon to be) no more, there needs to be a way to acquire SDL2. Since 20.04's version is older than our minimum required version (2.0.12), add it as an external.
Since Bintray is (soon to be) no more, there needs to be a way to acquire SDL2. Since 20.04's version is older than our minimum required version (2.0.12), add it as an external.