In order to build using prebuild NDK versions, this project must be initialized from a custom repo using:
mkdir android-games-sdk
cd android-games-sdk
Corp -> repo init -u persistent-https://googleplex-android.git.corp.google.com/platform/manifest -b android-games-sdk
AOSP -> repo init -u https://android.googlesource.com/platform/manifest -b android-games-sdk
repo sync -c -j8

Then:
./gradlew gamesdkZip
will build static and dynamic libraries for several NDK versions.

By default, the gradle script builds target archiveZip, which will use a locally installed SDK/NDK pointed
to by ANDROID_HOME (and ANDROID_NDK, if the ndk isn't in ANDROID_HOME/ndk-bundle).

It is also possible to build from a direct AOSP checkout, but then you won't be able to build for multiple
NDKs: archiveZip will still work but the gamesdkZip target will fail.