* CMake files are expanded to handle an Android target.
* Code that checks for specific defines or values like __FREEBSD__ || __LINUX__ now have an added condition to also check for __ANDROID__.
* Some tooling scripts to integrate adb into the Swift SDK.
* Some minor fixes elsewhere.
So, special support is a really minimal set of changes that any platform would need.
Also, there are also a bunch of support things for libICU which is not an official component on Android we are allowed.
Google has ripped most of the stuff they see as fluff for Android.
Edit: Any C and C++ API not listed as stable and public on the NDK docs is not guaranteed to exist in all devices.
On the other hand the Frameworks are quite expressive for applications, but one needs to use Java 6.5 or resort to third party solutions like retrolambda and Kotlin.