... on all platforms but MSVC, as it still has a number of unsolved warnings
in its `/Wall` level. Some of it might be valid, others might be overkill,
this needs further assessment and fixes. (We could also change the `extra`
level to `/W4` on MSVC if that's more meaningful.)
No need to waste time downloading all this when it's readily available :)
Also use the official action to setup Java 8.
Also build both architectures (armv7 and arm64v8) and generate the APK,
so we can upload it.
Remove now unused and outdated `misc/ci/android-tools-linux.sh`.
The base branch is hardcoded as an env variable as I couldn't find a simple
way to just get either `3.2` or `master`. But it's easy to change when we
branch off from `master` to a new stable branch, which doesn't happen often.
(There's `{{github.base_ref}}` but it's probably more verbose like
`ref/heads/master`, and only valid for PRs.)
