Fix build Android example project

[4brunu]

The Android example project it's not building anymore due to multiple incompatibilidades with the last Android Studio release 3.3.2 as today.
So I fix all the issues, because this was not letting me run the command make all with success.
Where it was possible I created a comment near the issue, showing the error, for future documentation on why things changed.

[4brunu]

@artwyman and @xianwen can you please take a look at this?
Thanks

[artwyman]

Are these issues are really tied to the updated Android Studio version or NDK version? I was aware of the NDK's move to clang, though I'm not sure if I want to take on the responsibility of making that update at the risk of breaking changes.

[4brunu]

@artwyman some changes are related to Android Studio and some to NDK, but the most relevant like clang are related to NDK.
I created this update, because someone that has the last version of Android Studio and NDK needs those changes to run the tests.

[artwyman]

I agree that updating to the latest version will be the most useful for more users. I'm going to hold off until I can test this against both old and new NDKs to understand the impact there, but plan to get it merged if I can work that out.

[artwyman]

After further testing this is less scary than I thought. It's able to build with NDK r11c (ancient version Dropbox has pinned) as well as r19c (latest non-beta) so I think it's safe to merge.