This defaults to the value of first_version, and should almost never
be used. This is only needed to work around platform bugs like
https://github.com/android-ndk/ndk/issues/265.
Test: Set `unversioned_until: "24"` for libGLESv3.ndk, readelf on the
android-23 and android-24 outputs to check for version info.
Bug: https://github.com/android-ndk/ndk/issues/265
Change-Id: Ie44b170daad692fdc98e7d7c5f10f9077930b8a9