Added android_native_app_glue module to raylib compilation instead of
compiling it as static lib at apk generation.

From 2019 64bit support will be mandatory to publish an Android app.
Google plans to require that new apps target Oreo (API level 26) in
August of 2018.

Now defaults to Clang, ARM64 and API 21

Note that only some lib versions have been updated

Not required any more!