Fix `make setup` on macOS.
Fix `make setup` on macOS.

Before, it always downloaded linux NDK no matter which platform you are
using. This way, `make setup` was actually able to break Android build
on macOS.

Signed-off-by: Igor Mandrigin <042dc4512fa3d391c5170cf3aa61e6a638f84342@mandrigin.ru>

status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react,status-im/status-react